The ill-fated boat was carrying nearly three times its recommended limit, police said, adding the accident occurred on the country's longest river - the Rajang - which flows in the interior of Borneo island in Sarawak state.
The boat, which is officially allowed to carry 67 persons, had more than 100 on board when it reportedly hit a rock and overturned in the swift flowing water.
The 181 survivors either swam ashore or were rescued by villagers, police said.
According to Star daily, the boat was on its way to Kapit and Sibu when it crashed onto a rock in the Rajang River.
Kapit district councillor Daniel Levoh said, "Many passengers were seen sitting on its roof which is not allowed.
