Alarms were triggered on board the International Space Station after the crew reported smoke and the smell of burning plastic.
The ageing space station has suffered a number of failures over the years and a Russian official recently warned of outdated hardware and failing systems, reports BBC.
These include air leaks, misfiring engines and cracks.
Russia's space agency, Roscosmos, said later that all systems were back to normal.
The smoke was detected during recharging of the station's batteries, the agency said, and the crew had now returned to "regular training".