RIO DE JANEIRO - At least 12 people died, 20 are still missing and another 50 injured when their boat sank in the Ariri river in the heart of the Amazonian region early Friday, official reports said.

More than 80 people were on board when the accident occurred at 0100 local time (0400 GMT) at some 500 meters from Cachoeira do Arari port in Brazil's northern state of Para, according to the local fire brigade.

At least five of the victims were children, according to the fire brigade, that is taking part in the rescue works together with two patrol boats and two speedboats from Brazil's Navy as well as several divers' teams.

Among the injured people, nine are in critical conditions, according to press reports.

The boat "Leao do Norte" (Lion of the North), used for transporting passengers in the Amazonian region, departed from Vila do Arapixi, in Marajo Island, and was destined for Belem, the capital city of Para state.

The cause of the accident is still unknown. Local authorities have begun an investigation.