The Russian space agency launched the first stage of the giant laboratory, on time, at 0640 GMT from Baikonur in Kazakhstan.

Proton launch is described by mission control

The "city in space", which will sit 402 kilometres above the Earth, will take several years and cost many billions of dollars to complete.

When it is finished, it will be so big - more than 100 metres across - that it will be visible from the ground.

The launch of the Proton rocket carrying the station's first module went without a hitch.

Successful delivery

The heads of the space agencies of 16 nations participating in the project watched the lift-off at the Baikonur cosmodrome from a distance of about five kilometres (3 miles).

Zarya is in a near-Earth orbit

It was some 20 minutes after the launch that officials were able to announce that the module, called Zarya, had been successfully delivered into orbit.

"The booster has separated," NASA spokesman Kyle Herring told reporters. "Zarya is on its own."

Zarya is a 12.5-metre-long, cylinder-shaped module which will provide the initial power, communications and propulsion for the space station

Storage facility

Later modules will take over these functions and Zarya will serve mostly as a storage facility, holding fuel and other supplies.

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Zarya has been put in a near-Earth orbit - its minimum distance to the ground is 185 kilometres - but this will be lifted over the coming days before the space shuttle Endeavour goes up to connect the second module, Unity.

The United States and Russia are just two of sixteen nations co-operating in this major scientific and technological project.