Two flights arrived at a Belgian air base outside Brussels on Monday carrying 226 people -- mainly Afghan employees of international missions and their families -- escaping the chaos in Kabul.

The flights came from Islamabad, the hub for Belgium's Operation Red Kite rescue mission, which is acting as an air link to Kabul. 

Four military flights from Kabul were due to ferry more Belgium-bound escapees to the Pakistani capital later in the day. 

The mission's first flight back to Belgian soil brought 193 vulnerable people at Melsbroek base, home of Belgium's 15th Air Transport Wing, in a chartered civilian Air Belgium Airbus jet. 

Families, many with small children and carrying only hand luggage to begin their new lives in Europe, were led to four grey buses to be taken to the Peutie military base under police escort for health checks and immigration processing.

Many of the arrivals huddled under red blankets as they queued for their buses under the rain and grey skies. One, a woman in a headscarf, waved to reporters as she disembarked. 

A second flight, this one on a Royal Netherlands Air Force military A330 transport, arrived shortly afterwards with 33 passengers, including at least one diplomat, according to officers at the air base. 

Only one bus was needed for the second flight, which was far from full.  

Foreign Minister Sophie Wilmes said Operation Red Kite has already brought 400 people from Kabul's airport, which was being secured by US and allied troops, and out to Islamabad for onward travel to Belgium.

"The situation remains volatile. Thank you to everyone for their tireless efforts," she tweeted.

Belgium is one of several NATO and EU member states that are scrambling to rescue vulnerable foreign staff and Afghan allies from Afghanistan since the Taliban overran the capital just over a week ago.