Eleven people are still unaccounted for in the northern part of Japan's main Honshu island, which was hit on Saturday by a powerful 7.2 Richter-scale earthquake that also killed 11 people.

The Japan Meteorological Agency said the rainy season was believed to have started in the region, raising concerns that small dams formed naturally by the quake would break and trigger mudslides. The region has experienced very little heavy rain since the disaster.

Rescuers searching for the missing had to pull out before sunset due to worries over mudslides, said a local official in the hard-hit town of Kurihara. "It started drizzling shortly after noon today (Thursday)," said the official. "We have to carefully study the weather forecast to decide what we can do tomorrow."

To prevent damage due to the rain, workers set up sensors in two upstream river locations to alert rescuers and people downstream to mudslides, he said.

The earthquake, which left 260 people injured, was the most powerful to strike inland in the tremor-prone nation in eight years.

Much of the damage was caused by landslides, rather than the initial tremor.

A low-pressure front hits the Japanese archipelago, except for the northern island of Hokkaido, every year in early summer, with the rainy season usually lasting around a month.

All rights reserved. � 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.