Security personnel and volunteers stand near the wreckage of burned passenger bus and oil tanker on the Herat-Kandahar highway on Sunday. AFP

"Twenty-one people were killed in a traffic accident between a passenger bus, a tanker and a motorbike" on a main highway through Grishk district in southern Helmand province, Mohammad Qasim Riyaz, a spokesman for the provincial governor, said.

Of the 38 people injured, 11 were seriously hurt, according to the provincial information department.

The accident occurred in the early hours of the morning on a key highway that sees traffic between the western city of Herat through southern provinces to the capital Kabul, provincial officials said.

The passenger bus was travelling from Herat to Kabul when it first collided with a motorbike carrying two people, killing both riders, Helmand traffic management officials said, according to the information department.

The bus driver lost control and crashed with a tanker truck travelling in the opposite direction, sparking a fire. The accident killed three people on the tanker and 16 bus passengers.

"When the bus hit the tanker, it pierced the tank, which burst into flames," said one of the survivors, Ghulam Sarwar, speaking to AFP at a hospital in provincial capital Lashkar Gah.

"The flames got bigger and bigger and all the passengers in the front were burned. But at the back a window was broken and people were able to escape by jumping out," he added.

"If the window hadn't been broken, every passenger would have been killed." Images shared by the information department showed charred, twisted metal scattered across the highway and the crushed cabin of the tanker.

Clean-up crews arrived on site quickly to remove the debris, according to officials.

Sarwar said the bus was full of people recently deported from Iran, with many Afghans sent back across the border through the Islam Qala crossing near Herat.

"Among them were children and women," said Sarwar, who hurt his foot leaping from the bus.

"They were screaming when they were burning. It was a horrible moment, my heart is broken." Another survivor, Mohammad Reza, said many of the passengers had been asleep when the accident happened around 3:00am (2230 GMT Saturday).

"There were screams and cries when the bus caught fire," he said, adding that some passengers in the last seven or eight rows were able to jump out the window, some injuring themselves. "Everyone was trying to escape and save themselves," he added.

Taliban government spokesman Zabihullah Mujahid expressed regret over the accident and wished the injured a quick recovery, in a post on X.

"We seriously ask drivers to be careful while driving and to follow traffic rules," he said.

Abdullah Afghan Mal, a senior health official in Parwan, said many of the dead included women and children who were badly burned.

"Among the dead it was very hard to identify who was a male and who was a female," he said.

Agence France-Presse