Crowds looking to flee Afghanistan flocked to its borders while long queues formed at banks on Wednesday, as an administrative vacuum after the Taliban's takeover left foreign donors unsure of how to respond to a looming humanitarian crisis.

The Islamist militia focused on keeping banks, hospitals and government machinery running after the final withdrawal of US forces on Monday brought an end to a massive airlift of Afghans who had helped Western nations during the 20-year war.

With Kabul's airport inoperable, private efforts to help Afghans fearful of Taliban reprisals focused on arranging safe passage across the land-locked nation’s borders with Iran, Pakistan and central Asian states.

At Torkham, a major border crossing with Pakistan just east of the Khyber Pass, a Pakistani official said: "A large number of people are waiting on the Afghanistan side for the opening of the gate."

Thousands also gathered at the Islam Qala post on the border with Iran, witnesses said.

"I felt that being among Iranian security forces brought some kind of relaxation for Afghans as they entered Iran, compared with the past," said one Afghan among a group of eight that crossed over.

More than 123,000 people were evacuated from Kabul in the US-led airlift after the Taliban seized the city in mid-August, but tens of thousands of Afghans at risk remained behind.

Germany alone estimates that between 10,000 and 40,000 Afghan staff still working for development organisations in Afghanistan have a right to be evacuated to Germany if they feel endangered.

The Taliban is talking with Qatar and Turkey over how to run Kabul's airport, according to French Foreign Minister Jean-Yves Le Drian, but it could take days or weeks to finalise those negotiations.

Uzbekistan's land border with northern Afghanistan remained closed, but its government said it would assist Afghans in transit to Germany by air, once flights resume.

In a resolution on Monday, the UN Security Council urged the Taliban to permit safe passage for those seeking to leave, but did not mention the creation of a safe zone, a step backed by France and others.

The Taliban have declared an amnesty for all Afghans who worked with foreign forces during the war that ousted them from power in 2001 for their refusal to hand over al Qaeda leader Osama bin Laden after the Sept 11 attacks on the United States.

Taliban leaders have also called on Afghans to return home and help rebuild, while promising to protect human rights, in an apparent bid to present a more moderate face than their first regime, known for its brutal enforcement of radical Islamic law.

The militia made similar promises upon seizing power in 1996, only to publicly hang a former president, ban women from education and employment, enforce strict dress codes and adopt a punitive approach to the people of Kabul.

One woman said she saw Taliban fighters beating women with sticks outside a bank in the Afghan capital on Tuesday.

"It’s the first time I’ve seen something like that and it really frightened me," the 22-year-old said, on condition of anonymity, because she feared for her safety.

No new government yet

The Taliban have yet to name a new government or reveal how they intend to govern, unlike in 1996, when a leadership council was formed within hours of taking the capital.

The foreign minister of neighbouring Pakistan, which has close ties to the Taliban, said on Tuesday he expected Afghanistan to have a new "consensus government" within days.

In the absence of a government in Kabul, Britain and India held separate talks with Taliban officials in Doha, amid fears that up to half a million Afghans could flee.

Washington said it would use its enormous leverage, including access to the global marketplace, over the Taliban as it seeks to get the remaining Americans and allies out of Afghanistan after its military withdrew.

High on victory and back in power, some Taliban leaders mocked the United States.

"Your power is gone, your gold is gone," Anas Haqqani, who has emerged as one of the group's most prominent leaders, said on Twitter.

Haqqani posted a photograph of himself holding discarded prison shackles on Wednesday as he toured Bagram prison, where he spent years kept in solitary confinement by US forces.

Still, Afghanistan desperately needs money, and the Taliban are unlikely to get swift access to the roughly $10 billion in assets mostly held abroad by the Afghan central bank.

"If the international community wants to prevent an economic collapse, one way would be to allow Afghanistan to gain limited and monitored access to its reserves," Shah Mehrabi, an economics professor at Montgomery College in Maryland who is on the board of the central bank, told Reuters.

"Having no access will choke off the Afghan economy, and directly hurt the Afghan people, with families pushed further into poverty."

Last week, the United States freed the way to continue the humanitarian aid effort despite Washington's blacklisting of the Taliban, a Treasury Department official told Reuters.

Pentagon spokesperson John Kirby also said the United States was mindful of the threat posed by ISIS-K, the Islamic State affiliate that claimed responsibility for last week's suicide bombing outside Kabul airport which killed 13 US troops and scores of Afghan civilians.