At least 150 people were killed when a lorry transporting oil burst into flames near the Pakistani city of Ahmedpur East.
A crowd had gathered reportedly to collect fuel leaking from the crashed tanker, when it caught fire.
Dozens are being treated in hospital.
It appears the tanker blew a tyre while rounding a sharp bend in the road.
The fire was sparked by a passer-by lighting a cigarette, a rescue services spokesman Jam Sajjad told the BBC.
An army spokesman, Major General Asif Ghafoor said army helicopters were dispatched to ferry casualties to hospitals.
Pakistan’s Dawn newspaper reports revealed that at least six cars and 12 motorcycles were burnt.
Police sources told Pakistani government news agency APP that the tanker had been carrying 25 000 litres of oil and had been travelling from Karachi to Lahore.