A government official says 85 people were killed when a fuel truck exploded in South Sudan's rural Western Equatoria state on Wednesday.

Presidential spokesman Ateny Wek Ateny said Thursday that 50 others were injured in the blast which took place in Maridi after the truck veered off the road.

Citing the accounts of local authorities, he said the taker was "full of petrol" that started to leak and residents were siphoning off fuel when someone lit a cigarette, sparking an explosion.

Ateny said the injured were taken to local hospitals which are overwhelmed.