At least 35 people were killed on Sunday when a bus collided with a fuel tanker and burst into flames in southern Afghanistan, in the latest road accident in the war-torn country.

Many of the victims, including women and children, were burned beyond recognition in the accident in Zabul province, one of the areas worst hit by the Taliban insurgency.

"The passenger bus was on its way from Kandahar to Kabul when it collided with a fuel tanker in Jildak area of Zabul," provincial governor Bismillah Afghanmal told AFP.

"In the accident, 35 people were killed and more than 20 others were wounded."

Some of the injured were rushed to hospitals in the provincial capital Qalat as well as in neighbouring Kandahar province, said Ghulam Jilani Farahi, deputy Zabul police chief.

The Kabul-Kandahar highway passes through militancy-prone areas and many bus drivers are known to drive recklessly at top speed so as not to get caught in insurgent activity.

"President Ashraf Ghani expressed deep sadness over the death of our countrymen in the accident," the presidential palace said in a statement.

"Ghani has ordered the relevant authorities to help the victims and their families as soon as possible," it added.

Afghanistan has some of the world's most dangerous roads, often in dilapidated condition, and traffic rules are seldom enforced.

Many in the country rely on old and rickety passenger vehicles and road accidents with high casualty rates are common.

In May 73 people were killed when two buses and an oil tanker burst into flames in a head-on collision in the eastern province of Ghazni.

And in April 2013 a bus hit a wrecked fuel tanker in the southern province of Kandahar, killing 45 people.

The World Bank last November signed off on a $250 million grant to upgrade roads crossing Afghanistan's Hindu Kush mountains, crucial trade links that are often closed in winter by snow.

Insecurity is growing across Afghanistan as the Taliban press on with their 15-year insurgency against the Western-backed Kabul government.

Afghan troops have struggled to stave off the nationwide attacks since NATO forces ended their combat mission at the end of 2014.