Nasa is considering a rare early return of its crew from the International Space Station over an unspecified medical issue involving one of the astronauts, after cancelling a planned spacewalk that had been scheduled for Thursday, the agency said.

A Nasa spokesperson said the astronaut with the medical concern, whom she did not identify, was in a stable condition on the orbiting laboratory.

"Safely conducting our missions is our highest priority, and we are actively evaluating all options, including the possibility of an earlier end to Crew-11’s mission,” the spokesperson said in a statement on Wednesday night.

Nasa said in an earlier statement it was “monitoring a medical concern with a crew member that arose Wednesday afternoon”.