SAO PAULO, BRAZIL - A boat ferrying more than 100 people home from a party sank in Brazil's Amazon region before dawn on Sunday, killing at least 12 and leaving dozens missing, rescue officials said.

The Comandante Sales capsized and swiftly sank in the Solimoes River, one of the Amazon's largest tributaries, Fire Lieutenant-Colonel Raimundo Rodrigues da Silva said. The vessel was taking passengers home from a party near the jungle city of Manaus.

It was unclear what kind of boat the Comandante Sales was or how many passengers it was equipped to carry - but most boats that move people across the Amazon region are large wooden ferries, sometimes with two stories.

The area has few roads.

Rescue workers recovered the bodies of 10 women and two men while several dozen others were unaccounted for, Lt-Col da Silva said, noting that it was unlikely the boat had carried a passenger list. Victims had not been identified.

Investigators were exploring what caused the boat to capsize. It may have been overloaded and many sleeping passengers trapped inside when it went down, he said.