A part of the International Space Station (ISS) was evacuated on Wednesday after a toxic substance leaked, the Russian Federal Space Agency said.

The incident happened in the US-sponsored part of the ISS, and all astronauts were safely brought to the station's Russian section, the agency said.

"The crew's safety was ensured thanks to the quick actions of the astronauts and ground control in Moscow and Houston," the agency said. It added that NASA was analysing the situation.

Russian news agencies reported that the substance was ammonia, which is used as a coolant on the station.

Currently the ISS is staffed with three Russians, two Americans and one female Italian astronaut.