Astronauts evacuated from space station area

Officials later said a false sensor reading or computer problem probably set off the alarm, rather than an actual leak of ammonia coolant. “No signs of a leak,” Nasa said via Twitter. “Controllers are assessing.”

In the meantime, the six crew members huddled safely on the Russian side of the orbiting outpost as Mission Control analysed the data.

“Hey everybody, thanks for your concern,” Italian astronaut Samantha Cristoforetti said in a tweet. “We’re all safe and doing well in the Russian segment.”

The scare occurred well into the station crew’s workday.

As alarms blared, the astronauts followed emergency procedures in turning off non-essential US equipment, taking cover in the Russian quarters, then sealing the hatches between the US and Russian sides.

Nasa said because of the possibility of leaking liquid ammonia – it is used to cool electronics – the entire crew was ordered over to the Russian side.

The three Russians, two Americans and the Italian Cristoforetti will remain there until further orders.