Widespread chaos punctuated by sporadic violence has gripped Kabul's airport, with Western troops and Afghan security guards driving back crowds, following the Taliban's takeover of the Afghan capital on August 15.

Countries that have evacuated some 58,700 people over the past 10 days were trying to meet the deadline agreed earlier with the Taliban for the withdrawal of foreign forces, a NATO diplomat told Reuters.

"Every foreign force member is working at a war-footing pace to meet the deadline," said the official, who declined to be identified.

Leaders of the Group of Seven (G7) countries - Britain, Canada, France, Germany, Italy, Japan and the US - will meet virtually on Tuesday to discuss the crisis, when British Prime Minister Boris Johnson is expected to push for a deadline extension.

Biden, who has said US troops might stay beyond the deadline, has warned the evacuation was going to be "hard and painful" and much could still go wrong.

Democratic US Representative Adam Schiff, chairman of the House of Representatives Intelligence Committee, told reporters he did not believe the evacuation could be completed in the days remaining "given the number of Americans who still need to be evacuated".

A Taliban official said on Monday an extension would not be granted, though he said foreign forces had not sought one. Washington said negotiations were continuing.

CIA Director William Burns met Taliban leader Abdul Ghani Baradar in Kabul on Monday, the Washington Post reported, citing unnamed US officials.

Britain's defence minister, Ben Wallace, said he doubted there would be a deadline extension.

But German Foreign Minister Heiko Maas said Germany was working with the US and Britain to ensure the NATO partners can fly civilians out after the deadline.

Many Afghans fear reprisals and a return to a harsh version of Islamic law that the Taliban enforced when in power from 1996 to 2001, in particular the repression of women and freedom of speech.

The top UN human rights official, Michelle Bachelet, said she had received credible reports of serious violations committed by the Taliban, including summary execution of civilians and restrictions on women and protests against their rule.

"A fundamental red line will be the Taliban's treatment of women and girls," she told an emergency session of the Human Rights Council in Geneva.

An Afghan diplomat from the US-backed government told the forum that millions of people feared for their lives amid reports of door-to-door searches while China's UN envoy said the US army and its partners should be held accountable for rights violations they committed in Afghanistan.

The G7 leaders could discuss taking a united stand on the question of whether to recognise a Taliban government, or alternatively renew sanctions to pressure the Islamist militant movement to comply with pledges to respect women's rights and international relations.

"The G7 leaders will agree to coordinate on if, or when, to recognise the Taliban," said one European diplomat. "And they will commit to continue to work closely together."

Leaders of the Taliban, who have sought to show a more moderate face since capturing Kabul, have begun talks on forming a government that have included discussions with some old enemies from past governments, including a former president, Hamid Karzai.

Biden has faced widespread criticism over the August 31 withdrawal, which was initiated by his Republican predecessor, Donald Trump, under a deal struck with the Taliban, and his opinion poll ratings have slipped.

While Western countries have been trying to get people out, humanitarian agencies are struggling to get aid in.

The World Health Organisation only has enough supplies in Afghanistan to last for a week, an agency official said.

Australian Associated Press