Nine people died and 40 others were injured in Boksburg, a city east of Johannesburg, when a fuel tanker exploded, emergency services said Saturday.

The tanker, transporting liquefied petroleum gas (LPG), "got stuck under a bridge" close to a hospital and houses on Saturday morning.

"We received a call towards 7:50 am (0550 GMT) telling us a gas tanker was stuck under a bridge. Firefighters were called to extinguish the flames. Unfortunately, the tanker exploded," William Ntladi, spokesman for the emergency services in the region, told AFP.

One of those injured was the driver who has been taken to hospital, he added.

Of the 40 injured, 19 are in a critical condition while 15 others are seriously hurt but in a stable condition.

Six firefighters were also lightly injured, Ntladi said.

There was no immediate information on those killed in the blast.

Videos on social media showed a huge fireball under the bridge, which the tanker appeared to have been too high to go under.

It was carrying 60,000 litres of LPG, which is used especially in cooking and gas stoves, and had come from the southeast of South Africa.