Taliban insurgents are involved in an ongoing attack on the military side of Kabul Airport, which houses a NATO base.

Attackers wearing suicide vests have occupied a tall building at the airport and are firing at the military facility.

There was at least one large explosion at around 4.30am and a gunbattle began with security forces, according to Police.

The part of the airport that houses NATO's operations hasn't been damaged, but authorities don't know the extent of the risk because it isn't known how many terrorist bombers there are. 

People in the area said the explosions sounded like rocket-propelled grenades, along with automatic weapons fire.

The explosions could be heard in downtown Kabul, a few miles away from the airport, located on the outskirts of the capital.

The US-led NATO coalition's joint command headquarters at the airport runs the day-to-day operations of the nearly 12-year-old war against insurgents. The airport's military side is also used for NATO transport and other aircraft.

The International Assistance Force's Joint Command said it was aware of an attack, but gave no further details.