International Space Station

This May 23, 2011 photo released by NASA shows the International Space Station at an altitude of approximately 220 miles above the Earth, taken by Expedition 27 crew member Paolo Nespoli from the Soyuz TMA-20 following its undocking. (AP photo/NASA)



Astronauts were forced to evacuate the U.S. section of the International Space Station on Wednesday after a chemical leak, the American and Russian space agencies said.

All crew were safe and had moved to the Russian side of the facility after the leak of "harmful substances," the Russian Federal Space Agency said on its official website. The U.S. section of the I.S.S. had been sealed off.

"The safety of the crew has been secured by prompt joint action by the US and Russian crewmembers, as well as by mission control staff in Moscow and Houston," said the head of the Russian Mission Control Center, Maksim Matyushin, in .

NASA confirmed to NBC News that the leak was ammonia. The space agency said the crew were safe and that it was in the process of coming up with a plan to deal with the leak.

The station is a collaboration of 15 nations working together in a state-of-the-art orbiting research facility.

The International Space Station's current crew consists of six researchers representing two expeditions.

Expedition 42 arrived on the ISS in September and consists of US astronaut Commander Barry Wilmore and Russian cosmonauts engineers Aleksandr Samokutyaev and Elena Serova, the first Russian female cosmonaut in 17 years.

Astronauts Commander Terry Virts of the US and Italy's onboard engineer Samantha Cristoforetti and Russian cosmonaut engineer Anton Shkaplerov make up Expedition 43.