Associated Press
In this Dec. 1, 2014, image provided by NASA taken during a training exercise, U.S. astronaut Terry Virts, left, assists European Space Agency astronaut Samantha Cristoforetti with emergency training aboard the International Space Station. Astronauts evacuated the U.S. section of the International Space Station and moved to its Russian module after a problem emerged Wednesday, Jan. 14, 2015.

CAPE CANAVERAL, Fla. — The astronauts are back in the American side of the International Space Station.

Early Wednesday, the crew fled to the Russian segment after an alarm indicated a possible toxic leak. But NASA later said there was no leak of the ammonia coolant and a computer problem likely set off the false alarm.

By Wednesday afternoon, the astronauts had returned to the U.S. side.

When the alarms went off around 4 a.m., the crew followed emergency procedures — slapping on oxygen masks, taking cover in the Russian quarters, then sealing the hatches between the U.S. and Russian sides.

At the same time, flight controllers at NASA's Johnson Space Center in Houston turned off non-essential equipment.