RIKUZENTAKATA, Japan—Hundreds of soldiers and police fanned out across this tsunami-ravaged city, as authorities redoubled efforts to recover the bodies of thousands still missing along Japan's northeast coast after the disaster.

Thousands of military personnel from the Japanese Self-Defense Force conduct a third massive search for the bodies of victims of the country's devastating earthquake and tsunami. Video courtesy of Reuters and photo courtesy of AP.

Troops in camouflage uniforms searched through heaps of rubble with the aid of heavy excavators equipped with giant claws capable of lifting tangled steel and concrete slabs, while police used shovels and their hands to dig through debris in downtown buildings.

The searchers recovered 27 bodies Monday in Rikuzentakata, according to a police official at the city's makeshift morgue in the gymnasium of an unused primary school. That is more than double the average number discovered daily last week.

Six weeks after a massive wall of water, set in motion by a magnitude-9 earthquake, slammed into Rikuzentakata on March 11, hundreds of local residents remain missing. Across Japan, the number is more than 11,000. More than 14,000 are confirmed dead.

In all, about 25,000 Japanese soldiers started an intensive two-day search operation up and down the northeast coast Monday. They were joined by naval and coast guard vessels and police forces across the region.

No national figures on the number of remains recovered in Japan on the first day of this latest operation were available late Monday.

The large number of missing has frustrated grieving families and municipal officials, and is slowing the pace of the cleanup as authorities delay widespread use of heavy machinery fearing buried bodies will be discarded.

Reaching some kind of conclusion to the search for bodies is seen as a critical step in kick-starting reconstruction projects.

Many people swept away by the waves last month, however, are unlikely ever to be found. After the Indian Ocean tsunami in 2004, tens of thousands of missing people were never recovered.

The soldiers and police scouring downtown Rikuzentakata had to contend with a hailstorm and heavy rain that turned lower-lying areas into shallow ponds. A military helicopter hovered low over the river as its crew searched the waters below.

"There are still many people missing, so we keep searching again and again," said Major Michihiro Saito, of Japan Ground Self Defense Force's Ninth Division. "We're tired. But compared to people who lost relatives and homes, we're doing OK."

Much of the ground in Rikuzentakata has been combed over multiple times. But the area is vast, and in some places towering tangles of wreckage obscure what lies beneath.

"It takes a long time to work through all the debris," said Masaki Odate, an inspector with a detachment of riot police from Tokyo who had joined the search. "When the machinery pulls off the top layers, sometimes bodies are inside."

Police found a woman's body inside the badly damaged building of the local hospital Sunday. She had been pinned under a heavy desk and metal cabinets on the first floor. Her body, hidden, had gone unnoticed in previous searches.

The woman is believed to have worked in the hospital, police said. And on Monday, police and soldiers were systematically emptying the building of debris, looking for a second female hospital employee still listed as missing.

Write to Gordon Fairclough at gordon.fairclough@wsj.com