At least 20 people were killed in a head-on collision between a truck and a bus ferrying workers to a mine in South Africa’s northern Limpopo province, authorities said Monday.

Construction company Murray & Roberts Cementation said 17 of its workers, who were being transported to the Venetia mine in Musina close to the Zimbabwe border, died in the accident Sunday. Four other workers were injured.

The company said it was offering support to the families of the deceased.

The workers were reportedly going to work on an underground project at a mine owned by mining giant De Beers.

Traffic officials were still on the scene of the accident on Monday to investigate the cause.

Provincial Transport Minister Florence Radzilani, who visited the crash site Monday, lamented the state of some of the trucks that travel on the roads.

"We always talk to our law enforcement officers and send out messages to these drivers to say they must make sure the vehicle is roadworthy so that you don’t put the lives of innocent people at risk," she said.

Radzilani said some truckers avoided roads where traffic officials are highly visible because some of the vehicles were unroadworthy or the drivers did not have valid permits.

"We are waiting on investigators but there are already allegations about the truck driver not having a license and the truck not being roadworthy," she told public broadcaster SABC.