At least 123 people were killed and scores injured in a fire that erupted after an oil tanker overturned in central Pakistan early Sunday and crowds rushed to collect fuel, an official said.

The tragedy came less than a day before Pakistan was due to begin Eid al-Fitr celebrations marking the end of the holy fasting month of Ramadan, with many roads crowded as people travel home for the holidays.

The tanker carrying 40,000 litres of fuel overturned on a main highway while travelling from Karachi to Lahore, near the town of Ahmedpur East in Punjab province.

Details were unclear but some witnesses suggested the tanker had suffered a burst tyre, said regional police chief Raja Riffat.

"When it turned over the residents of the nearby village of Ramzanpur Joya rushed to the site with buckets and other containers, and a large number of people on motorcycles also came and started collecting the spilling fuel," Riffat told AFP.

"After about 10 minutes the tanker exploded in a huge fireball and enveloped the people collecting petrol. It was not clear how the fire started."

Residents could be seen walking past blackened and twisted bodies piled by the side of the road. Earlier, television footage showed shooting flames and a thick plume of smoke as firefighters battled to extinguish the blaze.

The charred wreckage of dozens of motorcycles and cars could be seen scattered on the highway, along with kitchen utensils, pots, water coolers, jerrycans and buckets which victims had brought to collect the petrol.

Both Riffat and senior local government official Rana Mohammed Saleem Afzal, speaking to state television, said at least 123 people had been killed. Afzal said more than 100 were wounded.

"Many bodies could not be identified as they have been charred very badly," Riffat said.

Punjab provincial law minister Rana Sanaullah told private ARY television that DNA tests were being used to identify the dead.

He said the driver of the tanker had survived the crash and been taken into custody.

- Military aid -

Pakistan Motorway Police spokesman Imran Shah told AFP they received a call about the accident at around 6.30 am.

Motorway police raced to the scene and tried to keep people away from the tanker, he said, adding that they were ignored as residents continued filling their containers with fuel.

The military said it was sending army helicopters to evacuate the wounded and hospitals were put on high alert. The nearest burns centre is believed to be more than 150 kilometres away.

A doctor in Ahmedpur East, who requested anonymity as he was not authorised to speak to media, said more than 100 people had been brought to the local hospital with more than 80 percent burns before they were rushed to larger hospitals in Multan and Bahawalpur.

Prime Minister Nawaz Sharif expressed his grief and directed the government of Punjab province, run by his brother Shabhaz Sharif, to provide "full medical assistance".

Pakistan has an appalling record of fatal traffic accidents due to poor roads, badly maintained vehicles and reckless driving.

At least 62 people including women and children were killed in southern Pakistan in 2015 when their bus collided with an oil tanker, starting a fierce blaze that left victims burnt beyond recognition.

The country has also long struggled to contain a chronic energy crisis, with regular blackouts crippling industry and exacerbating anger against the government.

A series of deadly militant attacks across the country Friday unnerved many Pakistanis, with officials increasing the death toll Sunday to a total of 69 -- 51 dead in blasts in northwestern Parachinar, 14 killed in an attack targeting police in Quetta, and four police murdered in a drive-by shooting in Karachi.

Social media users Sunday posted messages of grief and solidarity with the victims of the oil tanker crash as well as Friday's attacks, as many prayed for a safe Eid.