Twenty-three people were missing in Borneo after an overloaded boat capsized in treacherous rapids on a jungle river, Malaysian police said.

Tuesday's accident occurred near the town of Belaga on Malaysia's longest river, the Rajang, which flows from deep in the sparsely populated interior of Sarawak, one of two Malaysian states located on Borneo island.

Sarawak police chief Acryl Sani Abdullah said 181 people had been rescued, but 23 were still unaccounted for when the rescue teams abandoned their mission for the evening.

"So far no bodies have yet been found. We stopped the operation because there is no light any more. We will resume our operation tomorrow," he told the AFP news agency.

The vessel was carrying nearly three times its recommended limit of 74 passengers, including many indigenous tribal palm oil and timber workers returning to their home villages for a harvest festival holiday, said Bakar Sibau, a district police chief in Sarawak state.

The overturned boat remained in the river and there were fears that some people may have been trapped inside. Acryl Sani said some may have been swept downstream and managed to climb ashore.

Boat 'struck rock'

Rom Kulleh, an aide to a local Belaga politician, told AFP by phone that he saw the overturned and mostly submerged boat in the river while flying over the area in a helicopter.

"The boat was stuck in the water. It was upside down," he said, adding that some of those rescued were plucked from the water by passengers aboard other boats plying the river.

Most passengers were believed to be heading home for the coming weekend's Gawai festival, a major cultural and religious observance for indigenous Borneo tribes that triggers heavy travel in Sarawak.

Officials said the boat, which set off at the Bakun dam, was heading downstream and was believed to have struck a rock while navigating one of many rapids on the 560-kilometre waterway.

Sarawak is Malaysia's largest state by area but also one of its least developed.

Boat operators often come under intense pressure from travellers demanding to be allowed on board so they can reach their destinations in time for the festival, police chief Bakar said.

"The operators are sometimes threatened with assault if they refuse to ferry passengers," he said.

Source: Agencies