Conservative radio host Glenn Beck says 1,200 Christians have been rescued from Afghanistan in a donor-funded evacuation.

A fundraiser launched by the Blaze founder has raised over $28m towards the mission.

Speaking on the Blaze, he said some of that included a loan he had signed for personally, and a "significant" donation given by journalist and TV host Bill O'Reilly.

In an Instagram update, Beck said a third plane full of evacuees had taken off on Tuesday.

"Now 1200 Christians evacuated and flown to safety. It has been a good day!" he wrote.

"Thank you for the outpouring of prayers and support! Because of The Power Of One people will LIVE. Wow!"

He added, "America does care! America does not leave her own and the most vulnerable behind. WE CAN DO IT AS THE POWER IS WITH THE PEOPLE. We are America not our government. When they can't do it, private citizens step to the plate."

The evacuations are being coordinated by the Nazarene Fund, a US non-profit that helps persecuted Christians and other minorities.

While the mission has been launched primarily to evacuate Christians, the Nazarene Fund said other religious minorities, American citizens and "vulnerable" people were among the people on the flights.

Nazarene Fund CEO Tim Ballard said in a Facebook update that the planes have taken the evacuees to an undisclosed "safe" country.

Last night he said that the non-profit had "many more planes" lined up to transport at-risk Afghans and US citizens out of the country.

"We're sending them as fast as we can, including some other kind of more asymmetrical strategies to pull other people out who didn't make it to the airport," he said, adding, "We are doing all we can."

In an earlier update, he said Christians found with a Bible app on their mobile phones or identified as such on their ID card will be "summarily executed".

Time is running out for the mercy flights, with US President Joe Biden saying the operation will not be extended beyond the 31 August deadline.

Two days ago, Ballard said there were an estimated 15,000 people crowded around Kabul airport looking for a flight out.

But he said there were still thousands more hiding out further afield from the airport and in need of rescue.

"Our Christian brothers and sisters, US citizens who we're in contact with, so this is far from over," he said.

In another video he said, "There are many Christian Afghanis who converted over the last two decades. Why? Because the US government provided freedom, the infrastructure, constitutional protections that allowed them to confidently become Christian and proudly put on their ID card that 'I'm a Christian'. Those ID cards are now their death warrants.

"When the Taliban sees that, they are summarily executed. If they try to get to the airport and they see even a Bible app on their iPhones, they are summarily executed."

There have been reports elsewhere of private investors paying ex-special forces operatives to go into Afghanistan to extract Afghans and their families.

The Alabama-based non-profit Ark Salus says it has raised over half a million dollars for its Operation On Wings of Eagles which aims to fly up to 5,600 Afghan soldiers and police officers out of Afghanistan before the August 31 deadline.

"We have a moral obligation to our fellow Afghan Warriors to safeguard them, their wives and children, and rescue them from Kabul, just as they have brought us home to our families," said Pete Quinn, CEO and Director of Ark Salus. This effort carries from immediate rescue action through long term advocacy for our Afghan brethren and their families—We will work earnestly with other international organizations to place, care for, and safeguard our Afghan families. We stand at the forefront when it counts the most in these trying times."