At least six people died and another 29 were injured Tuesday when a bus plunged off a bridge in southern Brazil for unknown causes, officials said.

The vehicle set out from the city of Sapiranga in the state of Rio Grande do Sul headed for Sao Paulo, but in the early hours crashed some 10 meters (33 feet) down a cliff.

The accident occurred outside Guaratuba, a city in Parana state, where the 29 injured, six of them in critical condition, have been hospitalized, doctors told Brazilian media.

Police said that the causes of the tragedy have not yet been established, but indicated that traces of oil were found on a curve just before the bridge, which could have brought on the accident. EFE