Thousands of Americans and Afghans are currently inside the airport trying to flee the country, and a massive crowd remains outside the gates. Many people have been out there in the sweltering heat for days, being gradually crushed by the weight of the crowd.

The US embassy in Kabul previously warned Americans it could not “ensure safe passage” to the airport for them.

In an “urgent announcement” today, it went further.

“If you or any of your family are at the airport, please leave and go home as quickly as possible,” the embassy said.

“Do not go back to the airport until the embassy removes this security alert.

“Because of potential security threats outside the gates at the Kabul airport, we are advising US citizens to avoid travelling to the airport and to avoid airport gates at this time unless you receive individual instructions from a US government representative to do so.”

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The chaos further undercuts US President Joe Biden’s goal of evacuating all American citizens and eligible Afghans by August 31.

And adding to the sense that the situation is spiralling out of control, senior US officials appeared to have no knowledge of the new alert from their own embassy when they fronted a Pentagon media conference this morning.

Asked about the advice urging Americans to stay away from the airport, General Hank Taylor was taken by surprise.

“You talked about guidance going out to not come. I’m not familiar with that directly,” Gen Taylor said.

“What you’re seeing out of our State Department colleagues, I think, is prudent notification to make sure that whatever movement there is to the gates from outside the airport is done as safely as possible, and that people have the information they need to make the best decisions for themselves going forward,” added Pentagon Press Secretary John Kirby.

Just yesterday, Mr Biden said he’d seen “no indication” that Americans were unable to get inside Kabul airport.

That claim was immediately contradicted by reporters on the ground in Afghanistan. Now it has been further contradicted by the US embassy.

According to the Pentagon, the US has evacuated 3800 people in the last 24 hours, and 17,000 people in the last week.

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It isn’t just the Americans struggling. Today Sky News UK’s chief international correspondent, Stuart Ramsay, filed a harrowing report on the British evacuation attempt.

Ramsay described the scene immediately outside the airport, saying it was “very different” from previous days and “turned chaotic in an instant”.

“At the front of the queue, people were being crushed to death,” he said.

“Paratroopers began pulling people from the mayhem, medics rushing from the next casualty to the next, then the next and the next. Crushed, dehydrated, terrified.”

Soldiers stood atop the walls spraying the crowd with a hose to try to cool people down, including “lots and lots of children”.

“Then what we had all feared began to happen,” said Ramsay.

“Soldiers started shouting for medics and stretchers as unconscious people were carried to the rear. The medics checked their vital signs and then covered the bodies in white sheets.

“It doesn’t matter where you look, it’s the same desperation: American soldiers, British soldiers, Spanish soldiers, German soldiers, Polish soldiers, pulling children and whole families from the pens and the crowds they’ve been kept behind for processing.”

In a separate report, the experienced correspondent described the view beyond the airport as “quite simply horrendous”, with “thousands, maybe tens of thousands crushed as far as the eye can see”.

“At the front, Taliban militants beat Afghans with canes,” he said.

“There is nothing the civilians can do and nothing paratroopers can do but hold the line. I’ve seen many bad things, but right now I can’t think of anything worse.”

Ramsay said he’d spent most of the day with tears in his eyes.

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Another British correspondent, The Independent’s Kim Sengupta, reported that four people had died within a period of two hours outside the airport, collapsing in the baking heat after hours of being crushed by the crowd.

Their bodies were placed along the side of the road to be collected by their families.

One of the Afghans Sengupta spoke to, a 22-year-old student named Samira, believed her life was in danger from the Taliban because she had been critical of conservative clerics.

“The Taliban started visiting our neighbourhood and taking a list of people. My parents told me I must leave for my own safety,” she told him.

“I knew I had to go. They can arrest me or, as I am a single woman, even marry me off to someone. It was very hard coming through the Taliban checkpoint.

“I don’t know what I’ll do if I get turned down. I can’t live under the Taliban, that would be impossible. I would rather be dead.”

At that moment Samira’s eyes fell upon the covered bodies on the side of the road.

“I didn’t mean that, I don’t want to die,” she said.

“Those poor, poor people and their families. I wonder if people in the world outside realise what is happening here?”