Japan launched a massive military rescue operation on Saturday after a giant, quake-fed tsunami killed hundreds of people and turned the northeastern coast into a swampy wasteland.

Prime Minister Naoto Kan said 50,000 troops would join rescue and recovery efforts following Friday''s 8.9-magnitude quake that unleashed one of the greatest disasters Japan has witnessed, a 23-foot (7-metre) tsunami that washed far inland over fields, smashing towns, airports and highways in its way.

Kan toured the Northern part of the country on Saturday to see the damage for himself.

The official death toll stood at 413, while 784 people were missing and 1,128 injured.

Police said between 200 and 300 bodies were found along the coast in Sendai, the biggest city in the area near the quake''s epicenter.

An untold number of bodies were also believed to be buried in the rubble and debris.

Rescue workers had yet to reach the hardest-hit areas.

Adding to the worries was the damage at the Fukushima Daiichi nuclear power plant, where two reactors had lost cooling ability. Because of the overheating, a meltdown was possible at one of the reactors, said an official with Japan''s nuclear safety commission.

Most of the 51,000 residents living within the danger area had been evacuated, he said.

More than 215,000 people were living in 1,350 temporary shelters in five prefectures, or states, the national police agency said.

Since the quake, more than 1 (m) million households have not had water, mostly concentrated in northeast.

The region continued to be jolted by tremors, even 24 hours later.

More than 125 aftershocks have occurred, many of them above magnitude 6.0, which even alone would be considered strong.

Technologically advanced Japan is well prepared for quakes and its buildings can withstand strong jolts, even a temblor like Friday''s, which was the strongest the country has experienced since official records started in the late 1800s.

What was beyond human control was the tsunami that followed.

It swept inland about six miles (10 kilometers) in some areas, swallowing boats, homes, cars, trees and even small airplanes.

Smashed cars and small airplanes were jumbled up against buildings near the local airport, several miles (kilometers) from the shore. Felled trees and wooden debris lay everywhere as rescue workers coasted on boats through murky waters around flooded structures, nosing their way through a sea of debris.

Basic commodities were at a premium. Hundreds lined up outside of supermarkets, and gas stations were swamped with cars.

The situation was similar in scores of other towns and cities along the 1,300-mile-long (2,100-kilometre-long) eastern coastline hit by the tsunami.