There were at least two explosions near Kabul's airport amid a huge and chaotic evacuation effort from Afghanistan on Thursday, the Pentagon said, with civilians and US service members among the casualties of what was described as a "complex attack".

US officials said they were concerned that further attacks could occur at the airport following the twin blasts, which health officials have said killed at least 60 people. The Taliban earlier said at least 13 were dead, including children. 

Islamic State claimed responsibility for the attack on Thursday, the group's Amaq News Agency said on its Telegram channel.

A suicide bomber from the Islamist militant group "managed to reach a large gathering of translators and collaborators with the American army at 'Baran Camp' near Kabul Airport and detonated his explosive belt among them, killing about 60 people and wounding more than 100 others, including Taliban fighters," it said.

At least 10 US troops are believed to have been killed in the blasts that rocked Kabul on Thursday, a US official told Reuters citing initial information that can change. US officials have said there are about 5200 American troops providing security at the Kabul airport.

The New Zealand Defence Force said all of its personnel were safe, and would issue an update later on Friday morning.

The attacks came after the United States and allies urged Afghans to leave the area because of a threat by Islamic State militants.

Pentagon spokesman John Kirby said one blast occurred near the airport's Abbey Gate and the other close to the nearby Baron Hotel. Two US officials said at least one of the explosions appeared to be from a suicide bombing.

"We can confirm that the explosion at the Abbey Gate was the result of a complex attack that resulted in a number of US & civilian casualties," Kirby said on twitter. "We can also confirm at least one other explosion at or near the Baron Hotel, a short distance from Abbey Gate."

The US Embassy in Kabul described "a large explosion" and said there had been reports of gunfire.

A source who was in touch with a witness by text message quoted that witness as saying there appeared to have been two separate but simultaneous attacks, one by a suicide bomber near buses lined up outside Abbey Gate, where the blast was followed by small arms fire.

The second occurred at Baron Gate, named after the nearby Baron Hotel. The source, speaking on condition of anonymity, quoted the witness as saying that children were among the casualties.

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The attacks came after the United States and allies urged Afghans to leave the area because of a threat by Islamic State.

A massive airlift of foreign nationals and their families as well as some Afghans has been underway since the day before Taliban forces captured Kabul on August 15, capping a swift advance across the country as US and allied troops withdrew.

The United States has been racing to carry out the airlift before its military is set to fully withdraw from the country by August 31. There was no indication from the White House that Biden plans to change the August 31 withdrawal target as a result of the attacks, a source familiar with the situation told Reuters.

Biden was in a meeting with security officials about the situation in Afghanistan, where the United States is in the final steps of ending its 20-year war, when the explosion was first reported, according to a person familiar with the matter.

Biden, Secretary of State Tony Blinken, Defense Secretary Lloyd Austin, Joint Chiefs of Staff Chairman General Mark Milley and Vice President Kamala Harris monitored events via video links.

In an alert issued on Wednesday, the US Embassy in Kabul had advised citizens to avoid travelling to the airport and said those already at the gates should leave immediately, citing unspecified "security threats."

A Western diplomat in Kabul said that areas outside the airport gates had been "incredibly crowded" again despite the warnings.

The United States and its allies have mounted one of the biggest air evacuations in history, bringing out about 95,700 people, including 13,400 on Wednesday, the White House said on Thursday.

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On Friday, Labour MP David Parker called the attacks tragic. 

"We're doing our best to get out those who've helped New Zealand in our operations over there, and some partner agencies, and are at risk of retaliation from the Taliban. But as you can see, it's just been very, very difficult. Tragic.

"By the hour it gets harder. The US has made it clear they're not going to defend the airport beyond the end of August, and they had been expecting… suicide attacks such as this, or other attacks."

National MP Simon Bridges had similar views, telling The AM Show the attack was "devastating" and "horrific".

"We need to do all we can to be repatriating these Afghanis who've helped us. Actually I think there's a case to do more than that potentially.

"But I do acknowledge that right now it's very unsafe, probably too unsafe, for New Zealand to be doing a lot on the ground without US forces being able to clear and have the airport safe for comings and goings."

Reuters / Newshub.