All US embassy personnel, including Ambassador Ross Wilson, were transferred to Kabul airport to await evacuation and the American flag was removed from the embassy compound, A U.S. State Department spokesperson said early on Monday.

Five thousand US troops are reported to have reached Kabul to secure the airport and taken over the air traffic control operations.

The United States started evacuating its diplomats on Sunday and had sent additional troops to help secure Kabul airport and the embassy.

TV channels showed helicopters evacuating US personnel from the embassy and smoke spiralling near the compound as important papers and sensitive information recorded on electronic devices were burnt to prevent them falling into Taliban hands. Other Western countries are also pulling their staff out of Afghanistan.

Also read: US embassy in Kabul burning secret papers & electronic devices as Taliban closes in

While the Taliban have taken over Kabul, US President Joe Biden has said his administration had told Taliban officials in Qatar that any action that put U.S. personnel at risk "will be met with a swift and strong U.S. military response."

But he also said an indefinite U.S. military presence was not an option.

Biden has authorized the deployment of 5,000 U.S. troops to make sure we can have an orderly and safe drawdown of U.S. personnel and other allied personnel."

This is an additional 1,000 men as earlier the number of troops approved for the evacuation was put at 4,000. The US has also flown a backup force to nearby Kuwait in case the situation gets out of hand and additional troops are required for an orderly draw down from Kabul.

Hundreds of Afghans invaded the airport's runways in the dark on Sunday night in a desperate attempt to catch one of the last commercial flights to leave the country before the US forces took control. 

Also read: Has Kabul turned out to be another Saigon moment for the USA?

More than 60 western countries, including the United States, Britain, France and Japan, issued a joint statement saying all Afghans and international citizens who wanted to leave the country must be allowed to depart.

"The Afghan people deserve to live in safety, security and dignity," the statement said. "We in the international community stand ready to assist them," the statement said.