The Japanese military pumped jets of water from special fire trucks into a damaged reactor at the stricken Fukushima nuclear plant Thursday in a desperate bid to bring down temperatures, as high radiation levels were reported outside the evacuation zone.

Japanese engineers were able to lay an external grid power line cable to nuclear reactor No. 2 at the crippled Fukushima complex, the International Atomic Energy Agency (IAEA) said Thursday.

Authorities plan to reconnect power to the reactor once the military finishes spraying water on the No. 3 reactor building.

High radiation levels have been detected 18.6 miles (30 kilometers) from the plant, beyond the 12.4-mile (20-kilometer) zone designated by authorities, broadcaster NHK reported.

The situation at the Fukushima nuclear plant remains “very serious,” the International Atomic Energy Agency said Thursday, adding there had been no major deterioration since Wednesday.

Japan’s science ministry said exposure to the levels detected for a period of six hours would be the equivalent of the maximum safe level a person could absorb in a year.

The US urged its citizens to evacuate from a radius of 50 miles from the plant, while Singapore’s government advised its citizens to evacuate areas which are within 62 miles (100 kilometers) of the plant.

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International Atomic Energy Agency chief Yukiyo Amano departed for Japan, where he said he hoped to visit the plant with a team of experts.

Chinook military helicopters dumped tons of water in a desperate bid to cool reactors crippled by the earthquake to prevent a catastrophic meltdown.

Fire engines were put into action to douse fuel rods inside reactors and containment pools to stop them from degrading due to exposure to the air and emitting dangerous radioactive material, AFP reported.

A spokesman for operator Tokyo Electric Power Company (TEPCO) said the situation was very severe. Cooling the reactors to prevent the situation becoming critical and making sure the containment vessels remained sound was now the priority, he said.

Three of the six reactors at the plant in northern Japan were relatively stable. “The first unit is relatively stable, for now,” Hidehiko Nishiyama, a senior official at the Nuclear and Industrial Safety Administration, said, adding that an emergency generator was providing power for cooling at reactors No. 5 and No. 6.

The radiation level around the plant’s buildings was about 3,000 microsieverts per hour, TEPCO said, compared to the safe level of 1,000 microsieverts.

TEPCO said it was concerned about overheating at the No. 3 reactor’s cooling pool, which was damaged in last Friday’s 9.0-magnitude earthquake and subsequent tsunami. The No. 3 reactor contains plutonium fuel, which is particularly harmful to humans if released into the environment.

Overheating has caused four hydrogen explosions and two fires at the plant as well as a partial meltdown at the No. 1, No. 2 and No. 3 reactors of the six-reactor facility, located about 155 miles (250 kilometers) northeast of Tokyo.

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TEPCO was working to restore power at the complex, Kyodo News reported, citing the country’s nuclear safety agency.

Construction started on a new power line to connect to the Fukushima plant’s water pumps so that workers will be able to cool fuel rods by channeling seawater into reactor pressure vessels, containment vessels and storage pools of spent fuel, Nikkei reported.

The power system — and emergency diesel-fueled generators — failed when the tsunami, with waves as large as 24 feet (7.3 meters), hit the complex and soaked electrical equipment about an hour after the earthquake rocked Japan.

The US Navy delivered special protective suits and masks to help workers struggling to contain damage.

The US Navy’s 7th Fleet said, “100 nuclear, biological, chemical firefighting suits and masks were delivered from the USS George Washington to the government of Japan this [Thursday] morning for use at the Fukushima power plant.”

France will send a plane carrying 95 tonnes (105 tons) of boron, an element that dampens radiation, to help Japan tackle the crisis at the Fukushima power plant, energy and industry minister Eric Besson said.

A UN forecast, cited by the New York Times Wednesday, revealed a radioactive plume spreading from the stricken nuclear reactors in Japan could hit southern California late Friday — however there is expected to be little health risk.

The projection, which is based on current wind patterns, says the plume will move across the Pacific from Japan before touching the Aleutian Islands on Thursday and then heading towards the US.

Radiation levels will dilute as the plume travels and experts have stressed that it would have extremely minor health consequences in the US. The direction could also change with shifting weather patterns.

“All the available information continues to indicate Hawaii, Alaska, the US territories and the US west coast are not expected to experience any harmful levels of radioactivity,” the Nuclear Regulatory Commission said Thursday.

Japan instructed local authorities Thursday to start screening food for radioactivity, the first time it has set radiation limits on domestically produced food, AFP reported.