Thousands of Afghans desperate to leave the country thronged Kabul airport where five people were killed on Monday after Taliban fighters seized the capital, prompting the US military to suspend evacuations to clear the airfield.

Crowds converged on the airport seeking to escape, including some clinging to a US military transport plane as it taxied on the runway, according to footage posted by a media company.

The United States temporarily halted all evacuation flights from Kabul to clear people who had converged on the airfield, a US defence official told the Reuters news agency.

The official, speaking on the condition of anonymity, did not say how long the pause would last.

Taliban officials have declared the 20-year war over and issued statements aimed at calming the panic that has been building in Kabul as the group, who governed from 1996 to 2001, routed the US-backed Afghan army as foreign forces withdrew.

President Ashraf Ghani fled the country on Sunday as the Taliban entered Kabul virtually unopposed, saying he wanted to avoid bloodshed.

It was not immediately clear how the five people died at the airport on Monday. A US official said troops had fired in the air to deter people trying to force their way on to a military flight that was set to take US diplomats and embassy staff out of the city.

One witness, waiting for a flight out for more than 20 hours, said it was unclear if the five had been shot or killed in a stampede. US officials at the airport were not immediately available for comment.