At least 20 people died and 15 others were injured when a bus overturned on the Pan-American Highway in southwestern Colombia on Saturday, police said.

The bus was traveling between the port city of Tumaco in Colombia’s southwest corner and Cali, 200 miles (320 kilometers) northeast, when the incident happened.

“Unfortunately, we have 20 fatalities,” said Captain Albertland Agudelo of the Narino Department Traffic Police.

A three-year-old girl and an eight-year-old boy were among the injured.

Investigators are looking for possible “mechanical failures in the braking system,” Colonel Oscar Lamprea, director of traffic and transport for the region, said in a message to reporters.

According to a preliminary report, the driver lost control after exiting a corner in a foggy area.

It took police and fire brigade rescue workers nine hours to right the vehicle, evacuate the injured and recover the dead.

Images obtained by AFP showed the bus with its roof collapsed and perched dangerously on the edge of a steep cliff.