RIO DE JANEIRO, Jan. 7 (Xinhua) -- At least seven people were killed and 15 others injured when a passenger bus overturned early Tuesday in the state of Piaui in northeastern Brazil, the Federal Highway Police said.

The accident occurred between the municipalities of Sao Goncalo do Gurgueia and Corrente in southern Piaui, when the bus, en route from Tiangua to Sao Paulo, veered off the road and overturned.

Preliminary reports suggest that a mechanical failure or delayed reaction by the driver may have caused the accident.

The bus driver and six passengers died at the scene, while eight women and seven men of various ages were injured, whose current health status remains unknown. ■