Both remaining US personnel and Afghans fearing the return of Taliban rule were seen climbing onto military aircraft.
Chinook helicopters had shuttled back and forth between the US embassy and airport all weekend to remove remaining staff.
The American flag has since been removed from the now-empty embassy and personnel are reportedly holed up at the airport.
The scenes drew comparisons with the departure of US forces and civilians from Saigon at the end of the Vietnam War, prompting flat-out denials from the White House.
"Let's take a step back. This is manifestly not Saigon,” Secretary of State Antony Blinken told ABC News on Sunday.
As darkness fell in Kabul on Sunday, gunfire was reported around the airport. Any US citizens remaining in Kabul were advised by the US embassy to shelter in place following the reports of gunfire.
In an emailed statement late Sunday evening, a Pentagon spokesperson explained that US forces remained in control of Afghanistan’s airport, and had assumed control of air traffic operations “supported by Afghan counterparts”. Commercial flights, while sporadic, are still leaving the country while US citizens continue to be evacuated.
“Several hundred civilians including personnel and private US citizens have been evacuated so far. We continue to build capacity to expedite processing for at-risk Afghan civilians. We are especially grateful for Canada’s generous offer to host 20,000 Afghans at-risk,” John Kirby told The Independent.
“As we have made clear, this is a narrowly-defined mission to safeguard the movement of civilians out of Kabul. Any threat posed to the mission will be taken seriously—and any attack on our people or on our operation will be met forcefully,” he continued.
Reports on Twitter indicated that some Americans remained in Taliban-controlled areas, unable to reach the safety of US forces at the airport which was blocked by heavy vehicle traffic.
Thousands of US troops were deployed to the county by President Joe Biden in recent days to safeguard the removal of Americans and Afghans who work for the US government. That number was increased by roughly 1,000 on Sunday via an order from the White House in response to the fall of the Afghan government.
Several thousand more troops are reportedly on standby in nearby Kuwait.
Top Afghan officials were reportedly among some of those who made it out on commercial flights from the country in the hours before their government fell.
Afghan President Ashraf Ghani fled the country on Sunday hours before his government fell apart.
Taliban officials have proclaimed that the “Islamic Emirate of Afghanistan” will succeed Mr Ghani’s government.
The militant group now controls every major city and all border crossings in the country.
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