Japan suspended operations to prevent the stricken Fukushima Dai-ichi nuclear plant from melting down Wednesday after a surge in radiation forced workers to take cover indoors.
Chief Cabinet Secretary Yukio Edano said work on dousing reactors with water was disrupted by the high radiation levels.
"The workers cannot carry out even minimal work at the plant now," Edano said. "Because of the radiation risk we are on standby," he said.
A spokesman from Tokyo Electric Power Co., the owner of the facility, said workers were told to remain inside until it was safe.
The country has ordered a nearby 140,000 people to seal themselves indoors after a series of explosions and fires at the plant. The latest fire, at the plant's No. 4 reactor, is under control, according to TEPCO, which blamed it on an earlier fire that hadn't been fully extinguished. But Japan's nuclear agency was unable to confirm that the blaze had been put out, and clouds of white smoke were billowing from the reactor, according to live video footage of the plant.
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The agency also reported that damage to the fuel rods at the No. 1 reactor were at 70 percent. Kyodo News added that 33 percent of the second reactor's fuel rods were also damaged.
Tuesday’s fire at the fourth reactor is thought to have damaged the reactor's suppression chamber, a water-filled pipe outside the nuclear core that is part of the emergency cooling system.
Officials said radiation levels in areas around the nuclear plant rose early Tuesday afternoon but appeared to subside by evening.
Early Wednesday, Japan abandoned plans to spray water from helicopters into an overheating spent fuel storage pool at the facility. A TEPCO spokesman said that helicopters were deemed impractical, but other options were under consideration, including fire engines. There were later reports that a boric acid drop was being considered.
Boric acid is "important because it captures radiation and helps prevent radiation from leaking," said Masami Nishimura, the nuclear safety agency spokesman.
He said the government had also ordered the utility company to immediately spray water on Unit 4.
Both units 1 and 3 have no roof after earlier blasts, making it easy to dump water onto them, he said. Unit 4 has holes in the building, allowing fire trucks to spray water inside, he said.
Boric acid contains boron, which helps slow nuclear reactions by absorbing neutrons, said Naj Meshkati, a nuclear power plant safety expert at the University of Southern California.
The International Atomic Energy Agency has established a 19-mile no-fly zone around the plant's perimeter -- a move that comes as the U.S. Navy said Tuesday they detected low levels of airborne radiation at Yokosuka and Atsugi bases, 200 miles away from the nuclear plant, according to Newscore.
"We have received so [much] support from across the globe," said Noriyuki Shikata, the Japanese prime minister’s spokesman, to Fox News' Bret Baier on Special Report. "U.S. forces in Japan have been actively been helping the Japanese people."
Fox News has confirmed that a small number of U.S. service members have been exposed to radiation Tuesday and are being treated with potassium iodide pills. A U.S. military official says the risk is manageable.
"While there was no danger to the public, Commander, Naval Forces Japan recommended limited precautionary measures for personnel and their families on Fleet Activities Yokosuka and Naval Air Facility Atsugi, including limiting outdoor activities and securing external ventilation systems as much as practical," a U.S. Navy statement said.
The U.S. Department of Defense said Americans on two military bases south of Tokyo were advised to stay indoors as much as possible.
Japanese officials told the IAEA that the reactor fire was in a storage pond and that "radioactivity is being released directly into the atmosphere." Long after the fire was extinguished, a Japanese official said the pool, where used nuclear fuel is kept cool, might be boiling.
"We cannot deny the possibility of water boiling" in the pool, said Hidehiko Nishiyama, an official with the economy ministry, which oversees nuclear safety.
The IAEA's head, Yukoiya Amano, urged the Japanese government to provide better information to the agency about the situation.
Experts monitoring the troubles at the plant say a lot of the radiation that's been emitted has apparently come in steam from boiling water -- instead of directly from fuel rods.
Kyodo News reports that the plant was unable to pump water into Unit 4 reactor's storage pool for spent fuel. That reactor had been shut down before the quake for maintenance.
If the water boils, it could evaporate, exposing the rods. The fuel rods are encased in safety containers meant to prevent them from resuming nuclear reactions, officials said, downplaying the risk of that happening.
"After explosions at both units No. 1 and No. 3, the primary containment vessels of both units are reported to be intact. However, the explosion that occurred ... at the Fukushima unit No. 2 may have affected the integrity of its primary containment vessel. All three explosions were due to an accumulation of hydrogen gas," the IAEA said in a statement.
But they acknowledged that there could have been damage to the containers. They also confirmed that the walls of the storage pool building were damaged.
France's nuclear watchdog is now warning the situation at Fukushima's No. 1 nuclear plant now rates at six on a seven-point scale of gravity, according to AFP.
"Right now it's worse than Three Mile Island," said Donald Olander, professor emeritus of nuclear engineering at the University of California at Berkeley. But it's nowhere near the levels released during Chernobyl.
The 1986 Chernobyl incident in the Ukraine was a level seven, while the 1979 accident at the Three Mile Island nuclear plant was a level five.
On Three Mile Island, the radiation leak was held inside the containment shell -- thick concrete armor around the reactor. The Chernobyl reactor had no shell and was also operational when the disaster struck. The Japanese reactors automatically shut down when the quake hit and are encased in containment shells.
In a nationally televised statement, Prime Minister Naoto Kan said radiation has spread from the four stricken reactors of the Fukushima Dai-ichi nuclear plant along Japan's northeastern coast.
"I worry a lot about fallout," said Yuta Tadano, a 20-year-old pump technician at the Fukushima plant, who said he was in the complex when the quake hit.
"If we could see it, we could escape, but we can't," he said, cradling his 4-month-old baby, Shoma, at an evacuation center.
The U.N. weather agency said Tuesday that winds are currently blowing radioactive material toward the ocean, and that there were "no implications" for Japan or countries nearby.
"All the meteorological conditions are offshore, there are no implications inshore for Japan or other countries near Japan," said Maryam Golnaraghi, who heads the weather agency's disaster risk reduction program.
A World Meteorological Organization spokeswoman warned, however, that the conditions "will fluctuate as the weather systems progress."
"We can't say over the next two to three days what is going to happen," she added.
The radiation fears added to the misery of millions who have spent four nights with little food, water or heating in ear-freezing temperatures as they deal with the loss of homes and loved ones. Up to 450,000 people are in temporary shelters.
Japanese police said Tuesday the death toll from Friday's 9.0 earthquake and tsunami has surpassed 3,000 people, with an estimated 10,000 dead. Officials continue to deal with search and rescue problems Tuesday as 5.8 and 6.1-magnitude quakes were felt in Tokyo minutes apart, according to the United States Geological Survey.
Asia's richest country hasn't seen such hardship since World War II. The stock market plunged for a second day and a spate of panic buying saw stores running out of necessities, raising government fears that hoarding may hurt the delivery of emergency food aid to those who really need it.
Japan's central bank injected $326 billion into money markets over the past three days to ease the impact of the devastation.
In a rare bit of good news, rescuers found a 70-year-old woman alive in her swept-away home four days after the tsunami flattened much of Japan's northeastern coast.
Afterward, officials just south of the area reported up to 100 times the normal levels of radiation, Kyodo News agency reported. While those figures are worrying if there is prolonged exposure, they are far from fatal.
Tokyo reported slightly elevated radiation levels, but officials said the increase was too small to threaten the 39 million people in and around the capital, about 170 miles away. Closer to the stricken nuclear complex, the streets in the coastal city of Soma were empty as the few residents who remained there heeded the government's warning to stay indoors.
"Please do not go outside. Please stay indoors. Please close windows and make your homes airtight," Chief Cabinet Secretary Yukio Edano told residents in the danger zone.
"These are figures that potentially affect health. There is no mistake about that," he said.
Some 70,000 people had already been evacuated from a 12-mile radius from the Dai-ichi complex.
Edano said the radiation readings near Tokyo had fallen significantly by the evening.
With snow and freezing temperatures forecast for the next several days, shelters were gathering firewood to burn for heat, stacking it under tarps and tables.
In North America, two Japanese automakers -- Subaru and Toyota -- are halting some production at factories to assess availability of car parts following the damage in Japan.
Subaru of America says it has suspended overtime at its plant in Lafayette, Ind, while Toyota is suspending overtime and production on Saturdays at all of its North American plants to assess the availability of parts.
The Associated Press contributed to this report.