The number of dead has risen to 140 from an accident Sunday morning when an oil-tanker truck overturned and later exploded in southern Pakistan, incinerating scores of people who had rushed to the accident site with buckets to collect the spilt oil, according to local authorities.

The number of dead could rise even further as some of those injured are in serious condition, said Saleem Afzal, a top district government official.

A highway patrol official said that the accident occurred early Sunday morning when a tanker truck carrying refined oil from Karachi to Lahore crashed and overturned.

Many of those killed were people who had rushed to the accident site and were trying to collect the spilled oil when the truck burst into flames.

"We warned the people but suddenly there was an explosion and everybody was engulfed in fire," said the highway police official of the accident in Bahawalpur, located about 550 kilometers south of Islamabad.

"People standing in fields nearby were also engulfed in the fire," said one motorist at the accident site.

Pakistan's GEO TV broadcast a picture taken by a bystander seconds before the truck burst into flames, showing a pool of petrol on the roadside and people collecting it in buckets. Several motorcyclists are also shown filling their tanks from the pool using glasses and other vessels.

Rescue workers said several bodies were so badly charred that they could only be identified through DNA testing.

Afzal said the seriously injured were taken by road to Multan nearly 100 km away where a hospital has a burn unit.

Pakistan Army personnel from a nearby garrison had reached the site and the provincial government and Pakistan Army had dispatched helicopters to shift the critically injured to the nearest hospitals, media reports said.

The accident occurred in the Ahmadpur Sharqi sub-district of Bahawalpur, and a majority of the victims were from the nearby village of Ramzan Joya, according to Afzal.