The death toll from a gas tanker that exploded in Johannesburg on Saturday has risen to fifteen, authorities said, from an earlier estimate of eight.

The blast, which tore the roof off the emergency department at the Tambo Memorial hospital, destroyed two houses, several cars and injured bystanders, occurred when the vehicle caught fire while under a low bridge on Christmas Eve.

"In terms of fatalities ... this number has now risen to 15," including three hospital staff members, Health Minister Joe Phaahla said late on Sunday.

Phaahla suggested that the death toll might later rise because of the nature of the injuries some survivors had sustained.

"We are told that of those who survived, many of them have quite severe burns, so we still have a long way to go," he said. (Reporting by Tim Cocks; Editing by Kirsten Donovan)