More than 6,000 people are confirmed dead or missing in Japan, four days after an earthquake triggered a tsunami that wiped out entire towns in the country's northeast.

Police said nearly 2,475 people were confirmed dead and 3,611 missing Tuesday. But with hundreds of bodies washing ashore, the death toll was expected to climb much higher -- possibly as high as 10,000.

Japanese Prime Minister Naoto Kan called it the greatest crisis the country has faced since the Second World War.

Friday's 9.0-magnitude earthquake has also left millions with little food or shelter, as temperatures drop to near-freezing levels overnight. Hospitals are overwhelmed with the injured and running out of medicine and supplies.

In Iwate prefecture, one of the most devastated areas of Japan, government official Hajime Sato said only 10 per cent of needed supplies had been delivered. Authorities were also running out of coffins to bury the dead.

In neighbouring Fukushima prefecture, officials say the town of Soma is at least one-third flooded and thousands of residents are missing. The local crematorium was unable to handle the large number of bodies.

"We have already begun cremations, but we can only handle 18 bodies a day. We are overwhelmed and are asking other cites to help us deal with bodies. We only have one crematorium in town," Katsuhiko Abe, an official in Soma, told The Associated Press.

CTV's Lisa LaFlamme said due to the rising death toll, the Japanese government has waived a rule that requires citizens to get approval from their local officials before they cremate or bury a body.

"The current situation is so extraordinary, and it is very likely that crematoriums are running beyond capacity," said Health Ministry official Yukio Okuda. "This is an emergency measure. We want to help quake-hit people as much as we can."

Rescue workers were trying to recover up to 300 bodies in Sendai, the capital of Miyagi.

Another 8,000 people in Otsuchi, in Iwate prefecture, are said to be unaccounted for.

Indonesian geologist Hery Harjono said Japan's death-toll projection was too conservative. He told The Associated Press it would be "a miracle really if it turns out to be less than 10,000."

Harjono noted that many victims may have been pulled out to sea, as happened when the 2004 tsunami struck Indonesia's Aceh province. About 230,000 people died in Indonesia, but only 184,000 bodies were ever found.

Meanwhile, aid organizations are trying to assist people in Japan's hardest-hit areas.

"Some of the greatest needs are food and water, temporary shelter, and World Vision will also be focusing on children and the psychological toll that this earthquake has had by setting up child-friendly spaces for them," Casey Calamusa, of World Vision, told CTV News Channel from Tokyo.

With files from The Associated Press