The explosion tore the roof off the emergency department at the Tambo Memorial Hospital.

The tragedy also destroyed two houses, several cars, and injured bystanders up to 500m from the scene in the city’s Boksburg suburb.

The vehicle caught fire under a low bridge. The truck driver has been arrested on suspicion of culpable homicide, police said.

“Of the 18 deceased people, nine are Tambo Memorial Hospital staff,” the Gauteng health department said in a statement.

President Ramaphosa said hospital patients and children were among the dead.

“The nation’s hearts go out to everyone affected by this devastating incident,” he added in a statement.

“While we await the outcome of investigations into this tragedy, this incident does call on all of us to show due care and to avoid risk when we are out on our roads.”