Multiple explosions in Kabul

The Russian Foreign Ministry said at least two people had been killed and 15 wounded.

Adam Khan, an Afghan waiting outside the airport, said the explosion went off in a crowd of people waiting to enter the airport. Mr Khan, who said he was standing about 30 metres away, said several people appeared to have been killed or wounded, including some who lost body parts.

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 was due to end, few appeared to heed the call.

Pentagon Press Secretary John Kirby confirmed the explosion on Twitter shortly before midnight (AEST).

French President Emmanuel Macron said the coming hours would “remain extremely dangerous in Kabul and at the airport”.

“We are confronted with a very tense situation and we are coordinating with our American allies,” Mr Macron said, adding that the situation at the airport had seriously deteriorated and the French Ambassador would not be staying in Afghanistan.

Over the past week, the airport has been the scene of some of the most searing images of the chaotic end of America’s longest war and the Taliban’s takeover, as flight after flight took off carrying those who fear a return to the militants’ brutal rule.

Already, some countries have ended their evacuations and begun to withdraw their soldiers and diplomats, signalling the beginning of the end of one of history’s largest airlifts. 

The Taliban have so far honoured a pledge not to attack Western forces during the evacuation, but insist the foreign troops must be out by America’s self-imposed deadline of August 31.

Throughout Thursday, warnings emerged from Western capitals about a threat from Afghanistan’s Islamic State group affiliate, which likely has seen its ranks boosted by the Taliban’s freeing of prisoners during their blitz across the country.

British Armed Forces Minister James Heappey told the BBC early Thursday there was “very, very credible reporting of an imminent attack” at the airport, possibly within “hours”. 

The US Embassy had warned citizens at three airport gates to leave immediately due to an unspecified security threat.

Australia, Britain and New Zealand also advised their citizens on Thursday not to go to the airport, Australian Foreign Minister Marise Payne saying the situation remained “highly volatile and dangerous”.

“Our clear travel advice is now, do not travel to Hamid Karzai International Airport and if you are in the area of the airport, moved to a safe location and await further advice,” Ms Payne said.

“Be aware of the potential for violence and security threats with large crowds.”There is an ongoing and very high threat of a terrorist attack.”

Taliban spokesman Zabihullah Mujahid denied that any attack was imminent in the wake of those warnings.

Belgian Prime Minister Alexander De Croo said his country had received information from the US and other countries about the “threat of suicide attacks on the mass of people”. 

The acting US ambassador to Kabul, Ross Wilson, said the security threat at the Kabul airport overnight was “clearly regarded as credible, as imminent, as compelling”. 

But in an interview with ABC News, he would not give details and did not say whether the threat remained. 

A while later, the blast was reported. US President Joe Biden has been briefed on the explosion, the White House says.

The UK Ministry of Defence said it was working urgently to establish what happened.

“Our primary concern remains the safety of our personnel, British citizens and the citizens of Afghanistan,” it said in a statement.

“We are in close contact with our US and other NATO allies at an operational level on the immediate response to this incident.”

– with agencies