Germany's defence minister on Tuesday urged NATO to learn lessons from its Afghanistan mission -- slammed as a "debacle" by critics, as allies struggled to pull off a difficult evacuation operation from the capital, Kabul.

Speaking ahead of an emergency meeting of NATO ambassadors, Annegret Kramp-Karrenbauer told German broadcaster ZDF "there's a lot that we have to work on within NATO".

"The question for us will be to what extent are we willing to carry the consequences for this, and to what extent we are prepared to take measures that up to this point we have left to the Americans," Kramp-Karrenbauer said.

NATO ambassadors are meeting on Tuesday to discuss the situation in Afghanistan, where Western allied forces are seeking to accelerate their evacuation operations.

In an illustration of the messy situation on the ground, German officials revealed that a German military plane left Kabul carrying just seven evacuees, while hundreds waited on the ground at the airport in the Afghan capital Kabul.

"Due to the chaotic situation at the airport and the regular exchange of fire at the access point yesterday, further German citizens and people to be evacuated could not be given access to the airport without the protection of the Bundeswehr [German army]," a spokesman for the German foreign ministry said in a statement on Tuesday.

"The retrieval of people located in the civilian part of the airport was not made possible by partners responsible for security at the airport."

German special forces travelling into Kabul on the same flight were at the same time deployed with the task of securing future evacuations.

The return to power of the Taliban follows the withdrawal from the beginning of May of 9,500 allied soldiers still present in the country, including 2,500 American troops.

Armin Laschet, the leader of Angela Merkel's ruling party and candidate to be the next chancellor of Germany, described the Afghanistan mission as "the biggest debacle" in NATO's history.

A number of other German notables expressed their dismay at Washington's decision to pull out, which precipitated the Taliban's return to power in Afghanistan.

Merkel herself alluded to a decision made "due to domestic politics" in the United States.