Fears of a nuclear catastrophe stemming from twin reactor meltdowns gripped Japan yesterday as earthquake and tsunami survivors recalled biblical scenes of devastation along the nation’s battered east coast that killed at least 2,000 people — and left more than 10,000 missing.

In the wake of Friday’s disasters, engineers at the Fukushima Daiichi plant in northeast Japan were frantically trying to cool down white-hot nuclear fuel, which triggered a blast that destroyed the containment vessel surrounding the No. 1 reactor — one of six that have failed around the country.

Four were injured in the explosion and one was killed in a crane accident at another damaged plant.

Nuclear-agency officials said seawater and boric acid were injected into the core afterward — “unusual and improvised” solutions to the crisis, said Mark Hibbs, a senior associate at the Nuclear Policy Program for the Carnegie Endowment for International Peace. The last-ditch effort will likely take more than a week.

“I would describe this measure as a ‘Hail Mary’ pass,” said Robert Alvarez, a former adviser to the Department of Energy.

The desperate measures came as Japanese officials admitted that the core of the plant had partially melted down after the fuel rods were exposed from a dip in coolant levels. Radiation was leaking from the facility, although levels, at one point above legal limits, dipped after the explosion.

And late last night, officials said that a partial meltdown was likely under way at the plant’s No. 3 reactor, which also lost its cooling system. Steam was vented to relieve pressure on the core.

As unimaginable disaster from a full meltdown loomed, an evacuation was ordered for more than 200,000 people living within a 13-mile radius of the plant.

“If the fuel rods are melting and this continues, a [full] reactor meltdown is possible,” said Nuclear and Industrial Safety Agency spokesman Yuji Kakizaki.

In the wake of the blast, the government tested thousands for radiation exposure and said it was preparing to distribute iodine to anyone living near other nuke plants to protect them against thyroid cancer.

At least 19 people were believed to have been exposed to radiation and the number of people exposed was expected to climb to 160.

At one point, the plant was releasing as much radiation each hour as one person absorbs from the environment in a year.

While Japan’s nuclear-safety agency tried to downplay the risk at the first Fukushima plant, experts warned that the situation at the reactor — built in the 1970s and the oldest online in the country — was extremely precarious.

“We’re in uncharted territory,” said Ken Bergeron, a physicist who used to work at Sandia National Laboratories.

With the containment building destroyed, all that stands between the core and the outside world is the reactor vessel, six inches of stainless steel.

“If the reactor vessel is breached . . . then this radioactive stuff starts coming out in copious amounts,” said Alvarez.

Tiny particles of radioactive strontium, iodine and cesium would be hurled into the air, according to The Wall Street Journal. But since the winds generally blow west to east in Japan, the fallout would likely bypass the dense population centers to the south, the paper said. Still, cleanup around the site could take up to two years.

Scientists also say fallout equal to the catastrophic level of the 1986 Chernobyl disaster is unlikely because the Japanese reactor uses water instead of graphite to cool the core. Graphite produces soot when it melts.

Also yesterday:

* The estimated death toll rose to 2,000, many of the victims believed drowned in the waves that breached an 800-mile stretch of coastline. As many as 10,000 people were feared missing.

* Some 20,800 buildings were destroyed, and among the homes still standing, around 5.6 million households were without power — a tenth of the total in Japan.

* In Sendai, the nearest city to the quake epicenter, where 300 bodies had been recovered from the beach by yesterday, survivors scrambled for food and water. Some 200 bodies were found in the city of Higashimatsushima.

* Prime Minister Naoto Kan announced that 100,000 military personnel had been assigned to rescue duties, along with 190 military aircraft and 25 ships already in place in the hardest-hit areas.

* Four trains that had been running along coastal lines were still missing as of yesterday, said the East Japan Railway Co. One, a bullet train, had 400 people on board. A cruise ship with 100 passengers was also missing, officials said.

* Kesennuma, a seaside fishing town of 74,000 people, was one-third under water.

* Toyota planned to suspend operations at all 12 plants tomorrow.

Struggle goes on

* Fukushima Daiichi nuclear plant, 150 miles north of Tokyo, on verge of melting down. Government orders evacuation of 51,000 people in 13-mile radius of plant.

* Tokyo: Many residents had trouble finding food yesterday, fearing they wouldn’t be getting supplies for days. Convenience stores were sold out of bread, dairy products were running low and gas sales were limited to 5.3 gallons per car.

* Minamisanriku: 9,500 people — half the town’s population — reported missing in double disaster.

* Fukushima: A new earthquake with a magnitude of 6.4 hit yesterday about 52 miles off the coastline.

* Sendai: Four passenger trains running in a coastal area of the Miyagi Prefecture were missing. Unknown how many people were on board.

* Kesennuma: Hundreds of fires burned through the night in this seaside fishing town of 75,000 people that is consumed by black smoke.