A three-man space crew from Italy, Russia and the United States has arrived at the International Space Station for a five-month mission.

Footage broadcast by Russia's space agency Roscosmos showed the Soyuz craft carrying NASA astronaut Randy Bresnik, Russian cosmonaut Sergey Ryazansky and Paolo Nespoli of the European Space Agency take off into the dusky sky from Kazhakstan's Baikonur cosmodrome.

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Six hours later, after orbiting Earth four times, the Soyuz docked with the space station. The hatches between them were to open later, after pressurisation and leak checks are carried out, according to the US space agency NASA.

The arrival of the three astronauts boosted the ISS back up to its full capacity of six for the first time since April, after Russia decided to cut the number of its cosmonauts to two.

NASA has responded to Russia's reduction by boosting the number of astronauts that will operate in its half of the ISS.

In total, four astronauts — Peggy Whitson, Jack Fischer, Bresnik and Nespoli — will now conduct experiments in the NASA-run segment, with Ryazansky joining Fyodor Yurchikhin to man the Russian section.

Bresnik said at a pre-launch press conference on Thursday that the extra member would help the crew conduct experiments and carry out repairs.

"There is a ton of science to do," he said ahead of the flight.

Bresnik — who is on his second flight — also praised the work of Whitson, Fischer and Yurchikhin, already aboard the orbital lab.

"They've really got their groove on. They are working very, very well. They have good technique and tempo," he said.

Ryazansky, 42, who is embarking on his third stint aboard the ISS said at the press conference that he would be taking a small gnome into space in tribute to a song beloved by his family.

Live footage broadcast on Roscosmos's website showed the toy gnome hanging inside the capsule as the trio prepared for takeoff.

At 60 years old and with 174 days logged in space, Nespoli is the most experienced of the three fliers, but the Italian made it clear his love for space travel hasn't faded over time with a tweet showing him pulling his space suit on Friday.

"Beam me up S…oyuz! Hitching another ride soon to the @Space_Station," he wrote.

Nespoli became the oldest astronaut onboard, edging Fyodor Yurchikhin, 59 and Whitson, 57.

But Whitson is the oldest female astronaut in the history of space exploration and has broken other records during her latest mission at the ISS.

In April, Whitson became the NASA astronaut with the most cumulative time spent in space, having already broken the record for spacewalks by a woman the month before.

Whitson was expected to return home in June with Russian Oleg Novitsky and Frenchman Thomas Pesquet, but had her mission extended into September by NASA in a decision connected to the Roscosmos crew reduction.

Roscosmos has said its two-man crew format will help it save costs while the ISS waits on the arrival of a long- delayed Multipurpose Laboratory Module that will generate enough work on board to justify a third cosmonaut on board.

The $100 billion ISS space laboratory has been orbiting Earth at about 28,000 kilometres (17,000 miles) per hour since 1998.

Space is one of the few areas of international cooperation between Russia and the US that has not been wrecked by tensions over Ukraine and Syria.