A giant cloud of hydrogen gas is racing towards a collision with the Milky Way, astronomers have announced.

Smith's Cloud, as it is known, may set off spectacular fireworks when it smacks into our galaxy in 20-40 million years.

It contains enough hydrogen to make a million stars like the Sun, say experts, and its leading edge is already hitting gas from our galaxy.

When it does hit, the cloud could indeed set off a new burst of star formation in the Milky Way.

Details of the work, by a team at the US National Radio Astronomy Observatory and the University of Wisconsin-Whitewater, were unveiled at the 211th meeting of the American Astronomical Society in Austin, Texas.