The Taliban are on the brink of victory in Afghanistan, after their fighters entered the capital Kabul and seized the presidential palace.
The government has collapsed, with President Ashraf Ghani fleeing abroad.
Kabul descended into chaos, as local residents and foreign nationals tried to escape.
For many Afghans it was a terrifying day that marked the return of Taliban rule almost 20 years after they were ousted by a US-led coalition.
At the airport, an eyewitness told the BBC staff had abandoned their desks and people were running to planes.
Kabul was the last major city in Afghanistan to hold out against the Taliban offensive, which began months ago but has accelerated in the space of days.
The group were able to seize control now that foreign troops have all but withdrawn.
US President Joe Biden has defended the withdrawal of American troops, saying he could not justify an “endless American presence in the middle of another country’s civil conflict”.
‘People are running and hiding’
The Taliban ordered their fighters to enter Kabul on Sunday, after earlier holding them back at the outskirts of the city.
The Taliban said the militants were going in to prevent chaos and looting after security forces left parts of Kabul.
Footage broadcast by television network Al Jazeera showed fighters inside the presidential palace, brandishing guns.
A spokesman for the group later told Al Jazeera: “The war is over.”
The Taliban’s advance into Kabul came after President Ghani fled. Details of his whereabouts remain unknown.
In a Facebook post addressed to Afghan citizens, Mr Ghani said he made the difficult decision to leave to avoid bloodshed in the capital city.
“The Taliban won victory in the judgment of sword and gun and they have responsibility to protect the honour, prosperity and self-respect of our compatriots,” he said.
The president was criticised by other officials for leaving.
“God will hold him accountable and the nation will also judge,” said Abdullah Abdullah, chairman of Afghanistan’s High Council for National Reconciliation.
There was panic in Kabul as the Taliban drew closer to victory. Residents headed for the airport, abandoning cars and making their way on foot in a desperate bid to get out of the country.
One 22-year-old student told the BBC that he had walked for more than five hours.
“My feet hurt, they have blisters and I’m finding it difficult to stand,” he said.
“Now that I’m leaving, I think about my family – they don’t have any way to escape. I don’t see a future.”
The US Embassy said there were reports of gunfire at Kabul’s airport, and warned its citizens to take shelter as “the security situation… is changing quickly”.
In the city centre, large queues formed at ATMs throughout the day as people sought to withdraw cash.
Local MP Farzana Kocha told the BBC that people did not know what to do, with some running or hiding in houses.
There were reports of fighting and injuries in the city’s Qarabagh district.
Taliban spokesman Suhail Shaheen told the BBC that people in Kabul had no need to worry and that their properties and lives were safe.
“We are the servants of the people and of this country,” he said.
A rush to evacuate civilians
The US has deployed thousands of troops to help remove its staff and the Afghans who assisted with its mission. Helicopters transporting embassy personnel could be heard over the city on Sunday, and there were reports of smoke rising near the embassy compound as important documents were destroyed.
About 600 British troops have been deployed to assist with their own withdrawal mission.
UK Prime Minister Boris Johnson said his priority was getting UK nationals and “all those who have helped the UK effort over 20 years” out of Afghanistan “as fast as we can”.
Other countries are also evacuating their nationals, scaling back their presence in Afghanistan and in some cases closing their embassies altogether.
Russia is planning to convene an emergency meeting of the UN Security Council to discuss the situation in Afghanistan.
It said it would not be closing its embassy because it has been provided with security assurances by the Taliban.