A boat ferrying tourists on a wetlands fishing trip sank in western Brazil on Sunday, leaving nine people missing, emergency workers said.

Thirteen people were safely retrieved before darkness forced the suspension of rescue efforts, said fire Capt. Alcides Domingues de Oliveira. In an earlier statement, rescue workers said "some bodies" had been found, but they later declined to confirm any deaths.

The boat had been carrying 22 people on a fishing trip in the Pantanal wetlands, among the world's largest. It sank for unknown reasons just before dawn, nearly an hour and a half after leaving its port in the state's Pocone region.

Witnesses said they heard a cracking noise just before the boat went down, according to Globo TV's website.