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An explosion Tuesday morning at a Japanese nuclear plant damaged by the country's devastating earthquake and tsunami has elevated the risk of more radiation leaks to “very high,” as the country struggles to respond to the mounting human disaster.
The Fukushima Dai-ichi facility's precarious state was underscored by the details trickling out in the wake of the blast at the Unit 2 reactor. It was the third explosion in four days at the nuclear plant, and the condition of the Unit 2 reactor is of greatest concern to authorities.
"The level seems very high, and there is still a very high risk of more radiation coming out," Prime Minister Naoto Kan said in a nationally televised statement.
Radiation has spread from the three reactors of the Fukushima Dai-ichi nuclear plant, Kan said, and he warned there are dangers of more leaks and told people living within 12 miles of the complex to evacuate and people within 19 miles to stay indoors to avoid radiation sickness.
A fire at a fourth reactor that was extinguished by Tuesday afternoon further escalated concerns, as Chief Cabinet Secretary Yukio Edano said more radiation had been released.
"Now we are talking about levels that can damage human health. These are readings taken near the area where we believe the releases are happening. Far away, the levels should be lower," he said.
Officials reported slightly higher radiation levels in Tokyo, but insisted that there was no health threat so far.
The government suspects the explosion early Tuesday may have damaged the reactor's suppression chamber, a water-filled tube at the bottom of the container that surrounds the nuclear core, so radiation could escape.
Also Tuesday morning, Japanese police said the official death toll from the earthquake and tsunami has risen to 2,414, with a big share of the deaths in Miyagi prefecture, where 1,254 people are confirmed dead.
The number of people officially missing is at 3,118. But regional officials said they believe that tens of thousands may have been swept away by the tsunami that devastated a long stretch of Japan's northeastern coast.
Meanwhile, the U.S. Geological Survey upgraded the quake from magnitude 8.9 to magnitude 9.0 after further review.
The troubles at the Dai-ichi complex began when Friday's massive quake and tsunami in Japan's northeast knocked out power, crippling cooling systems needed to keep nuclear fuel from melting down.
International scientists have said there are serious dangers from the damage to the Fukushima Dai-ichi facility but not at the level of the 1986 blast in Chornobyl. Japanese authorities were injecting seawater as a coolant of last resort, and advising nearby residents to stay inside to avoid contamination.
Tokyo Electric Power said some employees of the power plant were temporarily evacuated following Tuesday morning's blast.
The cascading troubles in the Fukushima Dai-ichi plant compounded the immense challenges faced by the Tokyo government, already struggling to send relief to hundreds of thousands of people along the country's quake- and tsunami-ravaged coast.
Of all these troubles, the drop in water levels at Unit 2 had officials the most worried.
"Units 1 and 3 are at least somewhat stabilized for the time being," said Nuclear and Industrial Agency official Ryohei Shiomi "Unit 2 now requires all our effort and attention."
The accidents -- injuring 15 workers and military personnel and exposing up to 190 people to elevated radiation -- have compounded the immense challenges faced by the Tokyo government as it struggles to help hundreds of thousands of people affected by twin disasters that flattened entire communities.
Across the region, many residents expressed fear over the situation.
People in the port town of Soma had rushed to higher ground after a tsunami warning Monday -- a warning that turned out to be false alarm -- and then felt the earth shake from the explosion at the Fukushima reactor 25 miles away. Authorities there ordered everyone to go indoors to guard against possible radiation contamination.
"It's like a horror movie," said 49-year-old Kyoko Nambu as she stood on a hillside overlooking her ruined hometown. "Our house is gone and now they are telling us to stay indoors.
"We can see the damage to our houses, but radiation? ... We have no idea what is happening. I am so scared."
Meanwhile, 17 U.S. military personnel involved in helicopter relief missions were found to have been exposed to low levels of radiation after the flew back from the devastated coast to the USS Ronald Reagan, an aircraft carrier about 100 miles offshore.
U.S. officials said the exposure level was roughly equal to one month's normal exposure to natural background radiation, and the 17 were declared contamination-free after scrubbing with soap and water.
As a precaution, the U.S. said the carrier and other 7th Fleet ships involved in relief efforts had shifted to another area.
While Japan has aggressively prepared for years for major earthquakes, reinforcing buildings and running drills, the impact of the tsunami -- which came so quickly that not many people managed to flee to higher ground -- was immense.
By Monday, officials were overwhelmed by the scale of the crisis, with millions of people facing a fourth night without electricity, water, food or heat in near-freezing temperatures.
The Associated Press contributed to this report.