A pair of massive debris clouds shot out in space on Tuesday night after two big communications satellites collided in the first-ever crash of two intact spacecraft in orbit.

NASA said it will take weeks to determine the full magnitude of the crash, which occurred nearly 800 kilometres over Siberia on Tuesday.

"We knew this was going to happen eventually," said Mark Matney, an orbital debris scientist at Johnson Space Center in Houston.

The collision was between an Iridium commercial satellite launched in 1997 and a Russian satellite launched in 1993 and believed to be nonfunctioning. The Russian satellite was out of control, Matney said.

The Iridium craft weighed 560 kilograms and the Russian craft nearly a tonne.

Iridium Holdings LLC has a system of 65 active satellites that relay calls from portable phones that are about twice the size of a regular mobile phone. It has more than 300,000 subscribers. The U.S. Department of Defence is one of its largest customers.

The company said the loss of the satellite was causing brief, occasional outages in its service and that it expected to have the problem fixed by Friday.

Iridium also said it expects to replace the lost satellite with one of its eight in-orbit spares within 30 days.

No one has any idea yet how many pieces of debris were created by the collision or how big they might be, Matney said.

"Right now, they're definitely counting dozens," Matney said. "I would suspect that they'll be counting hundreds when the counting is done."

With pieces the size of micrometres, the count will likely be in the thousands, he added.

Space shuttle shouldn't be in danger: NASA

NASA believes any risk to the International Space Station and the three astronauts aboard is low. The space station orbits about 430 kilometres below the collision course.

There also should be no danger to the space shuttle set to launch with seven astronauts on Feb. 22, officials said, but that will be re-evaluated in the coming days.

Nicholas Johnson, an orbital debris expert at the Houston space centre, said the risk of damage from Tuesday's collision is greater for the Hubble Space Telescope and Earth-observing satellites, which are in higher orbit and nearer the debris field.

There have been four other cases in which space objects have collided accidentally in orbit, NASA said, but those were considered minor and involved parts of spent rockets or small satellites.

Roughly 17,000 pieces of manmade debris are orbiting Earth, Johnson said.

The items — which are only counted and watched if they are at least 10 centimetres — are monitored by the U.S. Space Surveillance Network, which spotted the debris clouds on Tuesday.