Despite some signs of hope in the past week at Japan's troubled Fukushima Dai-ichi nuclear plant, conditions have taken an increasingly alarming turn, with a possible breach at one of the reactors and highly radioactive water found leaking from that and two other reactors.

Work was under way Saturday to inject fresh water into one unit, said Hidehiko Nishiyama, a spokesman for Japan's Nuclear and Industrial Safety Agency, or NISA, amid concerns about dumping large amounts of potentially corrosive seawater onto the reactors.

Radioactivity in seawater just outside one unit tested some 1,250 times higher than normal, probably from both airborne radiation released from the reactors and contaminated water leaked into the sea, Nishiyama said Saturday. Tainted groundwater is the most likely consequence of the incident.

One Fukushima government official said some commercial trucks were refusing to enter the area because of radiation fears, resulting in a shortage of goods.

A nuclear crisis that not long ago was described as serious but stable has now raised concerns of a greater meltdown, with the danger underscored Friday with two plant employees hospitalized after wading into water 10,000 times more radioactive than normal.

The Tokyo Electric Power Co. told Kyodo News that it has begun injecting freshwater into the Unit 1 and 3 reactors at the plant, despite radioactive water leaking from Unit 1, 2 and 3.

The National Institute of Radiological Sciences says that the two employees have likely suffered "internal exposure" in which radioactive substances have entered their bodies, according to Kyodo News.

Trouble at the nuclear plant began shortly after the country's devastating earthquake and tsunami, which knocked out power at the plant, impairing its cooling mechanisms.

The possible breach in Unit 3 might be a crack or a hole in the stainless steel chamber of the reactor core or in the spent fuel pool that's lined with several feet of reinforced concrete. The temperature and pressure inside the core, which holds the fuel rods, remained stable and was far lower than would further melt the core. 

A Japanese government official told residents within 19 miles of the crippled plant to evacuate Friday.

Chief Cabinet Secretary Yukio Edano told a news conference that the government asked leaders of affected municipalities to encourage people to leave the affected areas, according to Kyodo News.

A somber Prime Minister Naoto Kan sounded a pessimistic note at a briefing hours after nuclear safety officials announced what could be a major setback in the urgent mission to stop the plant from leaking radiation.

"The situation today at the Fukushima Dai-ichi power plant is still very grave and serious. We must remain vigilant," Kan said. "We are not in a position where we can be optimistic. We must treat every development with the utmost care."

The uncertain situation halted work at the nuclear complex, where dozens had been trying feverishly to stop the overheated plant from leaking dangerous radiation. The plant has leaked some low levels of radiation, but a breach could mean a much larger release of contaminants.

Kan apologized to farmers and business owners for the toll the radiation has had on their livelihoods: Several countries have halted some food imports from areas near the plant after milk and produce were found to contain elevated levels of radiation.

He also thanked utility workers, firefighters and military personnel for "risking their lives" to cool the overheated facility.

The alarm Friday comes two weeks to the day since the magnitude-9 quake triggered a tsunami that enveloped cities along the northeastern coast and knocked out the Fukushima reactor's cooling systems.

Police said the official death toll jumped past 10,000 on Friday. With the cleanup and recovery operations continuing and more than 17,400 listed as missing, the final number of dead was expected to surpass 18,000.

The nuclear crisis has compounded the challenges faced by a nation already saddled with a humanitarian disaster. Much of the frigid northeast remains a scene of despair and devastation, with Japan struggling to feed and house hundreds of thousands of homeless survivors, clear away debris and bury the dead.

A breach could mean a leak has been seeping for days, likely since the hydrogen explosion at Unit 3 on March 14. It's not clear if any of the contaminated water has run into the ground. Radiation readings for the air were not yet available for Friday, but detections in recent days have shown no significant spike.

But elevated levels of radiation have already turned up in raw milk, seawater and 11 kinds of vegetables, including broccoli, cauliflower and turnips. Tap water in several areas of Japan -- including Tokyo -- also showed radiation levels considered unsafe for infants, who are particularly vulnerable to cancer-causing radioactive iodine, officials said.

The scare caused a run on bottled water in the capital, and Tokyo municipal officials are distributing it to families with babies.

Previous radioactive emissions have come from intentional efforts to vent small amounts of steam through valves to prevent the core from bursting. However, releases from a breach could allow uncontrolled quantities of radioactive contaminants to escape into the surrounding ground or air.

Government spokesman Yukio Edano said "safety measures may not be adequate" and warned that may contribute to rising anxiety among people about how the disaster is being managed.

"We have to make sure that safety is secured for the people working in that area. We truly believe that is incumbent upon us," the chief Cabinet secretary told reporters.

NISA spokesman Hidehiko Nishiyama said later that plant operator Tokyo Electric Power Co. was issued a "very strong warning" for safety violations and that a thorough review would be conducted once the situation stabilizes.

Another strong aftershock struck off Japan's northeastern coast Friday. A magnitude-6.4 earthquake hit close to the epicenter of the massive March 11 earthquake and tsunami, the United States Geological Survey says.

The Associated Press contributed to this report.