The International Space Station (ISS) crew has been asked to seek shelter in the docked SpaceX Dragon as concerns over an air leak in Russia's module persist.
The warning was issued as a precaution while the Russian crew works to fix cracks in the transfer tunnel.
NASA has urged its astronauts to prepare for evacuation if the situation worsens.
Air leaks in Russia's Zvezda service module have been a concern for several years, with cracks causing a slow pressure drop in the transfer tunnel.
Roscosmos has recorded an increase in air leaks from about a pound of air per day to two pounds, prompting NASA and Roscosmos to work together to find a permanent solution.
