Two underwater robots operated by a joint US-Japanese team have searched a bay in northeast Japan for bodies of victims swept away by a tsunami nearly six weeks ago, officials said Thursday.

Although the Micro-ROV robots failed to spot any corpses in the search on Tuesday and Wednesday, they found that the fishing port of Minami Sanrikucho was free of major underwater obstacles and could be reopened soon.

"The water in the port is still so murky that it is very difficult to inspect visually," said local fishery promotion official Akihiro Dazai.

"The robots' sonar and video cameras could check what it was like underwater," he told AFP by telephone. "We've confirmed that fishing boats can reach unloading berths without a major hindrance."

The backwash of the tsunami, which followed a 9.0-magnitude quake on March 11, was found to have dragged steel and lumber frames of buildings to the edge of a breakwater where they posed no danger to fishing vessels in the port famous for its autumn salmon haul.

Town mayor Hitoshi Sato told local media: "The fishery industry is a pillar of our recovery plan. The search result has given us a boost to reopen the fishing port at an early date."

The quake and tsunami have left more than 27,000 dead or missing and put a nuclear power plant in danger of a catastrophic meltdown.

Of the 18,000 people in Minami Sanrikucho on the rugged Pacific coast in Miyagi prefecture, some 450 were killed and 640 others went missing. Some 3,880 houses were washed away.

The search was conducted by the International Rescue System Institute, a Japanese nonprofit organisation led by Tohoku University professor Satoshi Tadokoro who specialises in studying disaster rescue robots and systems.

It was joined by the US Center for Robot-Assisted Search and Rescue led by Robin Murphy of Texas A and M University.

The joint team moved Thursday to another tsunami-devastated town of Rikuzen Takata to the north to conduct a similar search there on Friday and Saturday.

The robots are 40 centimetres (16 inches) high by 66 wide and 66 long and are remotely operated.