The US Air Force said on Tuesday that it was investigating the circumstances surrounding human remains that were found in the wheel well of one of its C-17s that flew out of Kabul amid the chaos of the Taliban taking over the Afghan capital.

Images circulated on social media earlier this week of Afghans desperate to leave Kabul rushing toward a C-17 and clinging to its side.

A separate video showed what appeared to be two people falling from a military plane as it flew out of Kabul.

In a statement, the US Air Force said that a C-17 aircraft landed at Kabul's airport on Monday and was surrounded by hundreds of Afghan civilians.

"Faced with a rapidly deteriorating security situation around the aircraft, the C-17 crew decided to depart the airfield as quickly as possible," the statement said.

It added that the US Air Force's Office of Special Investigation was reviewing information about the aircraft and the "loss of civilian lives".

At least five people were killed in Monday's chaos as thousands packed into Kabul's airport, rushing the tarmac and pushing onto planes in desperate attempts to flee Afghanistan.

One witness told Reuters he had seen the bodies of five people being taken to a vehicle. Another witness said it was not clear whether the victims were killed by gunshots or in a stampede.

Tolo News reported a higher count with at least 10 people killed and several wounded in the mayhem. It said the casualties were caused both by the warning shots fired by US soldiers in an attempt to control the situation and a stampede that ensued.

Meanwhile, senior US military officials said the chaos had left seven people dead, including some who fell from a departing American military transport jet.