RIO DE JANEIRO - At least 11 people were killed and another 11 injured Monday afternoon in the Brazilian city of Rio de Janeiro, after a passenger bus plunged over a cliff, Brazil's Federal Highway Police said.

The bus with 29 passengers on board was traveling from Itaperuna in Northeast Rio de Janeiro state to Rio when it skidded off the highway in the afternoon near the town of Guapimirm in a mountainous region. So far what had caused the accident is still unknown.

The bus driver was among the victims, and the injured have been taken to nearby hospitals by local rescue units and the country's Civil Defense officials.

Highway traffic was blocked to facilitate rescue efforts, as fire brigades were also involved.