A Russian Soyuz rocket with three astronauts on board blasted off from Kazakhstan on Wednesday for the International Space Station, where they are set to raise the labs crew to six for the first time.

Belgian Frank de Winne, Canadian Robert Thirsk and Russian Roman Romanenko lifted off from Russia's Baikonur cosmodrome in Kazakhstan at 11:34 BST for a two-day journey to the orbiting station.

This will be the first time the ISS will have six permanent members on board. After a crew rotation due in October, Winne will take over as commander for Expedition 21 to the space station.

The new crew members will join Russian cosmonaut Gennady Padalka, Nasa astronaut Michael Barratt and Japanese astronaut Koichi Wakata.

NASA says in the future, the space station could hold up to as many as 13 people, as the crew hosts short-term visitors.

The Soyuz TMA-15 is set to dock with the space station at 13:36 BST this Friday.

This trip aims to prove the station can support six people for a long duration, said Thirsk.

What we'll do over the next months will be to prepare for future space exploration, De Winne told the Associated Press.