At least six people have been killed and three others are missing after flash floods from torrential rains struck Indonesia’s main island of Java.

The National Disaster Mitigation Agency said rivers on the slopes of Mount Arjuno overflowed their banks on Thursday and their muddy waters inundated five hamlets in Kota Batu, a city in East Java province.

It said 15 people were swept away and six were later rescued.

The agency chief, Ganip Warsito, said heavy rains are expected to continue until February, partly because of a La Nina weather pattern.

Rescuers retrieved a body near Brantas river basin late on Thursday and five more bodies were found on Friday, officials said. Efforts are ongoing to find the three missing people.

Relief efforts were hampered by blocked roads covered with thick mud and debris.

Photos and videos released by the agency showed a damaged bridge, and houses and cars covered in thick mud.

Authorities are beginning to evacuate people in affected areas to government shelters, a spokesman said.

Severe flooding was also reported in other areas of the country but no casualties were reported.

Seasonal rains frequently cause flooding and landslides in Indonesia an archipelago of 17,000 islands where millions of people live in mountainous areas or near fertile flood plains.

The latest major floods were in April, when Tropical Cyclone Seroja triggered landslides and flooding that killed at least 183 people on Indonesia’s side of the Island of Timor, which the country shares with East Timor.

Another 42 people were found dead on East Timor’s side of the island.

The cyclone damaged thousands of homes and thousands of people were displaced.