At least 123 people were killed when a lorry transporting oil burst into flames near the Pakistani city of Ahmedpur East, local officials say.
A crowd had gathered reportedly to collect fuel leaking from the overturned vehicle when it caught fire. Dozens are being treated in hospital.
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.
Army helicopters were dispatched to ferry casualties to hospitals, army spokesman Major Gen Asif Ghafoor said in a tweet.
Pakistani media have published pictures from the scene, showing charred bodies and vehicles. There are fears that the death toll could rise further.
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 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, they said, about 8km (five miles) from Ahmedpur East, in Punjab’s Bahawalpur district.
“People living in roadside villages, carrying domestic pots rushed to the scene to collect oil and they also made phone calls to their relatives living in other villages to immediately come to collect oil,” the sources said.
Traffic police had tried in vain to keep the crowd away from the tanker as people, including women and children, continued collecting oil in pots, the sources said.
“Suddenly, [a] huge fire erupted in the oil tanker which engulfed all people standing around the vehicle,” the police sources added.
Emergency services struggled to find burn units to treat the injured, APP says.
Ahmedpur Sharqia Health Center and Bahawal Victoria Hospital have no such units but some casualties were brought to Nishat Hospital Multan and others were being moved to hospitals in the city of Bahawalpur, about 50km away.