At least 123 people were killed when a lorry transporting oil burst into flames near the Pakistani city of Bahawalpur, local officials say.
Unconfirmed reports suggest the tanker had been speeding when it overturned.
People smoking at the scene may have sparked the fire, Pakistan's Geo TV reports, quoting eyewitnesses.
The country's roads are notoriously dangerous, with poor vehicle maintenance and reckless driving contributing to the problem, correspondents say.
Army helicopters were dispatched to ferry casualties to hospitals, army spokesman Major Gen Asif Ghafoor said in a tweet.
At least six cars and 12 motorcycles were burnt, Pakistan's Dawn newspaper reports.
Some victims may only be identified by DNA sampling as bodies were badly burned in the incident, reports say.
'Police appeals ignored'
Police sources told Pakistani government news agency APP that the tanker had been carrying 25,000 litres (5,500 gallons) of oil and had been travelling from Karachi to Lahore.
It slipped off a road and overturned in the Kachi Pul area, about 8km (five miles) from the town of Ahmedpur Sharqia, they said.
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