The toll from a magnitude-8.9 earthquake in Japan could exceed 10,000 in the hardest-hit prefecture of Miyagi alone, police said on Sunday, as other officials tried to reassure the public that reactors at two damaged nuclear power plants posed no immediate danger.

"I have no doubt" that the death toll would rise above 10,000 in the prefecture, public broadcaster NHK quoted police chief Takeuchi Naoto as saying.

About 800 deaths had been confirmed so far in Miyagi and other areas in northeastern Japan, which were hit Friday by the quake and a tsunami. No contact could be established with about 10,000 residents of the town of Minamisanriku.

Police said earlier that more than 2,000 people had been killed or were unaccounted for in the affected regions, the Kyodo News agency reported.

A municipal official in Futaba town in Fukushima prefecture told Kyodo that about 90 percent of the houses in three coastal communities had been washed away by the tsunami.

About 390,000 people have fled their homes, many of them finding a place to stay at the more than 1,400 emergency shelters set up in schools and community centres, NHK said.

Prime Minister Naoto Kan doubled the number of soldiers sent to areas hit by the quake and tsunami to 100,000 as rescue workers were struggling to reach some of the affected areas with many roads blocked by debris.

"I ask for utmost efforts to save the lives of as many people as possible," Kyodo quoted Kan as saying after a meeting of the government's emergency disaster headquarters. "We will put all-out efforts into rescuing people who have been isolated."

Drinking water was transported to quake-hit regions by truck, and witnesses said residents were rushing to stock up on supplies at supermarkets and petrol stations, buying food and heating oil.

A top government official, meanwhile, said there were no problems with a damaged reactor even if the likelihood of a partial core meltdown could not be ruled out. Because of diminishing levels of cooling water at reactor number 3 of the Fukushima I power plant, a small-scale, partial meltdown might have taken place but, because water levels have been restored, that danger had been contained, chief Cabinet secretary Yukio Edano said.

Edano said there was no danger for nearby residents even if an explosion occurred because the reactor's containment vessel could withstand such a blast.

Reactors at the Fukushima I and II plants, 240 km north of Tokyo, lost their cooling functions after power and backup generators were cut off by the quake, operator Tokyo Electric Power Co. said.

On Saturday, a water vapour blast damaged the building housing the number 1 reactor, injuring four people. At least 19 people have been exposed to radioactivity, Kyodo said.

About 200,000 people have been evacuated from a 20-km safety zone around the two plants.

Further south, residents remained unconcerned. "Why should I flee?" Taduo Tayama, 60, of Chiba prefecture asked. "At the moment, the wind direction is favourable, but even if it turns, I'm not worried because outside the 20-km radius, everything is fine."

Railway links to the quake-hit regions are to remain closed, Japan Rail said, but it resumed operations in the Tokyo metropolitan area. Highways were also closed.