Two Russian cosmonauts stepped out of the International Space Station on Thursday in a spacewalk due to last six hours, Russia's mission control centre said.

Oleg Kononenko and Anton Shkaplerov opened the door to the Pirs space module and began work on the exterior of the ISS, the centre said in a statement.

During the spacewalk, the cosmonauts were to move a crane arm attached to the Pirs module to another module attached to the ISS, the centre added.

There are currently six men aboard the orbiting space station; three Russians, two Americans and a Dutchman.

The ISS, which orbits 350 kilometres (about 219 miles) above the earth's surface, is permanently occupied by a group of international researchers.

It circles the earth every 90 minutes traveling at 28,000 kilometres per hour.