The European probe Philae is on course to make the first ever landing on a comet after separating from its mother ship.

Philae ejected at around 0835 GMT (1935 AEDT), said European Space Agency flight operations director Andrea Accomazzo.

• Europe to make history with comet landing

“We see it in telemetry,” he said, amid cheers and relieved applause from members of the team.

Touchdown by the 100kg robot lab is expected after about seven hours.

A robot lab bearing 10 instruments, Philae is designed to carry out experiments on Comet 67P/Churyumov-Gerasimenko, racing towards the Sun at a distance of more than 500 million kilometres from Earth.

Comets are believed to be pristine clusters of ice and carbon dust, holding secrets on the origins of the Solar System – and possibly of life on Earth – 4.6 billion years ago.

If all goes well, Earth will receive a signal saying Philae has landed.

“Now, it’s down to the laws of physics. We’re on the way to the surface,” said ESA’s senior science advisor, Mark McCaughrean.

“I don’t have fingernails, so I won’t be biting them.”

Philae is meant to settle down at a gentle 3.5km/h, firing two harpoons into a surface that engineers fervently hope will provide enough grip.

Ice screws at the end of its three legs will be driven into the low-gravity comet to stop the probe bouncing back into space.

A final check found an apparent malfunction with a small gas thruster on top of Philae which is supposed to fire at the same time, providing a downward push, said Stephan Ulamec with the German aerospace firm DLR.

Conceived in the 1980s, the 1.3 billion euros ($A1.95 billion) Rosetta project was approved in 1993.

The orbiter, carrying Philae, was hoisted into space in 2004 but needed more than a decade to reach its target in August this year.