Meltdown fears intensify after new reactor blast and fire (VIDEO) (UPDATES)

BOSTON and TOKYO, Japan — Large amounts of radiation leaked into the air after a third reactor at an atomic power plant experienced an explosion and a fourth caught fire Tuesday morning in Japan, intensifying fears of a nuclear disaster in the wake of a devastating earthquake and tsunami that is thought to have left more than ten thousand people dead.

Prime Minister Naoto Kan announced that radiation spread from four reactors at the Fukushima Dai-ichi nuclear plant, 150 miles north of Tokyo, and warned anyone nearby to stay indoors.

"The level seems very high, and there is still a very high risk of more radiation coming out," Kan said in a nationally televised statement, reports the AP. "We are making utmost efforts to prevent further explosions and radiation leaks."

The hydrogen explosion at the No. 3 reactor of Fukushima Dai-ichi power plant injured 11 people, Reuters said. The blast damaged the reactor building and was felt 25 miles away. Reports said white smoke was seen billowing from the building.

The latest explosion was thought to be at the No. 2 reactor of the plant, and the fire at the No. 4 reactor, which had been unoperational. The No. 1 reactor was hit on Saturday.

AP reported that fuel rods in all three reactors at the plant appeared to be melting after falling water levels left them exposed. It quoted Chief Cabinet Secretary Yukio Edano saying: "Although we cannot directly check it, it's highly likely happening."

But the U.N.'s atomic watchdog, the International Atomic Energy Agency, said there was no sign of a full-scale meltdown, AFP reported. A meltdown would involve the radioactive core breaching containment walls.

By the end of Monday in Japan, it was the No. 2 reactor that was facing the most critical danger, according to the New York Times:

"An acute crisis developed late Monday at reactor No. 2 of the plant, where a series of problems thwarted efforts to keep the core of the reactor covered with water — a step considered crucial to preventing the reactor’s containment vessel from exploding and preventing the fuel inside it from melting down."

The plant was plunged into crisis after safety measures that kicked in following Friday’s 8.9 magnitude earthquake were affected by the powerful tsunami that washed ashore, engulfing vast tracts of northeastern Japan.

In their desperation to reduce the reactor's temperature, engineers have resorted to pumping in an untested mixture of seawater and boric acid. Authorities have declared an exclusion zone within a 15 mile radius of the plant and evacuated 210,000 people.

The death toll from the disaster continued to grow. About 2,000 bodies have been found washed up on the shores of Miyagi prefecture, which bore the brunt of the disaster, Kyodo said. About 1,000 were found on the Ojika Peninsula, and another 1,000 in the town of Minamisanriku, it said.

Authorities have said the death toll is expected to exceed 10,000, with at least 9,500 still unaccounted for in the coastal town of Minami Sanriku.

International efforts to help survivors were being hit radiation leaking from Fukushima. Low levels of radioactivity were found on 17 U.S. Navy helicopter crew members after they conducted relief missions from the USS Ronald Reagan, an aircraft carrier dispatched to provide help.

CNN said the U.S. Navy had repositioned ships and planes from its 7th Fleet — based in Japan — after detecting low-level contamination in the air and on its aircraft.

Japan’s Prime Minister Naoto Kan has said the earthquake, tsunami and nuclear threat have left his country facing its biggest crisis since the Second World War.

In a televised address to the public, Kan appealed to the country to come together in their time of crisis, and predicted the arrival of a Japanese-style New Deal sparked by huge demand as it recovers from the disaster.

“This is the worst crisis in Japan’s 65-year postwar history,” Kan said. “All of the people of Japan face a test as to whether they can overcome it. Together, I think we will.”

The disaster has left Japan's already fragile economy reeling. There has been major damage to key industries, with electronics giants Toshiba and Sony shutting down factories and automakers Nissan, Honda and Toyota halting production lines at the cost of millions of dollars a day.

There are more problems to come. Electricity suppliers on Monday began the first of what could be weeks of rolling power cuts affecting Tokyo to conserve energy following damage to supply networks and the shut down of nuclear reactors.

The blackouts, which will affect the city's heavily-used rail network, had been scheduled for earlier, but was postponed after citizens responded to a request to unplug appliances, significantly lowering demand, the Japan Times reported.

As grim details of the disaster continued to unfold, tales of miraculous survival brought brief moments of joy.

A Japanese rescue team Sunday managed to save the life of Hiromitsu Shinkawa, a 60-year-old man who survived the tsunami by clinging to the top of his roof. Shinkawa, found close to 10 miles out at sea, told his rescuers: "I thought today was the last day of my life."

— Barry Neild, Hanna Ingber Win