The Islamic State group has claimed responsibility for two suicide bombings that have killed US troops and innocent families waiting to escape Afghanistan.

At least 60 people are dead, including children, and scores more are in hospital after the twin attacks on crowds of people outside Kabul Airport.

The first explosion occurred late on Thursday (local time) near the Abbey Gate entrance to the airport and the second hours later at or near the Baron Hotel near the entrance, the US has confirmed.

Islamic State Khorasan (ISIS-K), an affiliate of militants who previously battled US forces in Syria and Iraq, said it was behind the twin blasts.

Pentagon spokesman John Kirby described it as a “complex attack” that has resulted in a number of US and civilian casualties.

“A number of others are being treated for wounds,” Mr Kirby said.

“We also know that a number of Afghans fell victim to this heinous attack…our thoughts and prayers go out to the loved ones and teammates of all those killed and injured.”

The US is yet to confirm the death toll but said 12 Americans had been killed and 15 other troops wounded.

Estimates of the total dead and wounded differed, and were rising quickly.

The Morrison government said there were no Australian casualties.

Defence Minister Peter Dutton confirmed Australian forces departed Kabul after the decision to complete a final airlift on Thursday.

“It’s a horrible, horrible day,” he told the Nine Network on Friday.

“I just grieve, like every decent person would, at the loss of life and in particular for us, the loss of the American lives.”

One explosion went off in a crowd of people waiting to enter the airport, according to Adam Khan, an Afghan waiting nearby. He said several people appeared to have been killed or wounded, including some who lost body parts.

Two bombs detonated near the airport. Photo: AAP

US President Joe Biden spoke from the White House, hours after the blasts. In a voice shaking with emotion, he said the US would hunt down those responsible.

He has asked the Pentagon to develop plans to strike back.

“We will not forgive, we will not forget. We will hunt you down and make you pay,” Mr Biden said.

He promised US evacuations would continue. He gave no indication of a change in Tuesday’s US pullout target.

“I have also ordered my commanders to develop operational plans to strike ISIS-K assets, leadership and facilities. We will respond with force and precision at our time, at the place we choose and the moment of our choosing,” Mr Biden said.

In a video aired on Thursday morning, Islamic State claimed responsibility for the attack. Photo: Twitter

Western forces who have been facilitating the evacuation at the airport were quick to confirm no casualties among their number, including Turkey, the UK, Germany and Italy.

World leaders condemned the attacks.

“I can confirm there has been a barbaric terrorist attack, series of attacks in Kabul, on the airport or the crowds at the airport, in which members of the US military have very sadly lost their lives and there have been many Afghan casualties,” British Prime Minister Boris Johnson said.

French President Emmanuel Macron said talks with the Taliban about the situation were already underway.

Thousands of Afghans have gathered at the airport for days trying to flee the country following the Taliban takeover.

Western nations warned Thursday of a possible attack on Kabul’s airport in the waning days of a massive airlift, as thousands of Afghans desperate to flee Taliban rule continued to flock to the gates.

Several countries urged people to avoid the airport, where an official said there was a threat of a suicide bombing. But just days – or even hours for some nations – before the evacuation effort ends, few appeared to heed the call.