A bus veered off a bridge in Nigeria’s northern state of Kano, killing at least 22 athletes returning home from a sports festival and leaving several other passengers injured.

Axar.az informs via AP, the cause of the accident, which happened on Saturday, was not immediately known. The athletes had taken part in the Nigerian National Sports Festival in the southern state of Ogun over the last week.

The driver appeared to lose control of the bus and the vehicle, with over 30 passengers, plunged off the Chiromawa Bridge on the Kano-Zaria expressway, according to Abba Kabir Yusuf, the governor of Kano.

Survivors of the crash were taken to a local hospital for treatment.

Yusuf said the athletes, who were accompanied by their coaches and sporting officials, were representing Kano at the sports festival, a major multi-sports event that bringing together athletes from the country’s 35 states every two years.

The governor declared Monday a day of mourning for the state. The families of the victims are to receive 1 million naira (about $630) and food supplies as support, Kano’s deputy governor, Aminu Gwarzo, said.

Road accidents are frequent in Africa’s most populous country, in part due to poor road conditions and lax enforcement of traffic laws.

In March, at least six people died near Nigeria’s capital of Abuja after a trailer crashed into parked vehicles and burst into flames.