Nearly 25,000 Japanese troops will Monday start a massive new search for bodies along the Pacific coast where some 12,000 people are still missing after the earthquake and tsunami, the military said.

Some US forces will join the 24,800 soldiers and members of Japan's Coast Guard and police for the third search since the disaster struck on March 11, devastating towns along the northeast.

"They will broadly cover the Pacific coast, areas around major river mouths and other tsunami-hit places," said a spokesman for Japan's Joint Staff.

In the past two major operations they found total 438 bodies, the defence ministry said.

More than 14,000 people were killed in the disaster and some 12,000 are still missing.

In a separate operation launched last Monday, some 2,500 Japanese troops have been searching for bodies within the 30-kilometre (19-mile) evacuation zone around the crippled Fukushima nuclear plant.

Officials from the local livestock department will also enter the 20-kilometre no-go zone around the plant to inspect the condition of the thousands of cattle, pigs and other animals abandoned as farmers fled the area.

"We haven't had any idea what it is like in the area now. This will be the first time we've entered the zone," said an official of Fukushima prefecture's livestock department.

Some animal rights activists who have entered the area have said there are a considerable number of cattle and other livestock dying.

"When we find dead animals, we will cover them with calcium hydroxide (caustic lime) due to sanitary concerns," the official said.

"We will slaughter those dying after getting permits from owners if they say it's too cruel to leave them like that."

Local officials will also check on the condition of horses that many in Minamisoma city, north of the plant, keep for the community's traditional folk festival, he said.

The no-go zone around the plant came into effect Friday, with police erecting checkpoints to prevent people returning to their homes within the high-radiation area. There is a wider 30-kilometre area where people have been encouraged to leave.