US and Russian astronauts have scrambled to temporarily patch a hole allowing air to leak from the International Space Station (ISS).

The leak, thought to have possibly been caused by a collision with a small meteorite, was detected on Thursday (AEST), resulting in a loss of cabin pressure.

The air leak was traced to a hole about 2mm in diameter, located in the most recent Russian Soyuz spacecraft capsule to dock at the space station.

NASA said the space station crew taped over the hole Thursday night, slowing the leak.

Flight controllers were monitoring the cabin pressure while working to come up with a better, long-term solution.

If not fixed, controllers estimated the craft would have run out of air in around 18 days.

NASA and Russian space officials have stressed the six astronauts are in no danger.

Depressurisation is among the most dangerous occurrences aboard the ISS.

NASA said that it started to notice depressurisation problems while the astronauts were asleep.

“As flight controllers monitored their data, the decision was made to allow the Expedition 56 crew to sleep since they were in no danger,” the agency said in an update.

“When the crew was awakened at its normal hour this morning, flight controllers at Mission Control in Houston and at the Russian Mission Control Centre outside Moscow began working procedures to try to determine the location of the leak,” it said.

The leaking Soyuz – one of two at the ISS – arrived at the orbiting lab in June with three astronauts on board.

The leaking Soyuz craft is expected to ferry three astronauts back to earth. Photo: NASA

The craft is expected to ferry the astronauts back to Earth in December, and also serves as a lifeboat in case of an emergency.

A NASA spokesman said it was premature to speculate on whether the three astronauts may have to return to Earth early if the leak, even as small as it is, cannot be stopped.

The hole is located in the upper section of the Soyuz, which does not return to earth, according to NASA.

The 400-km high outpost is home to three Americans, two Russians and one German. Orbital debris, even the tiniest speck, is a constant threat to spacecraft.

-with AAP