A piece of space junk has forced the three space station astronauts to seek emergency shelter.

For about an hour, the American and two Russians had to hunker down in their Soyuz spacecraft, which is docked to the International Space Station, in case they had to make a quick getaway.

The fragment from an old Russian weather satellite ended up passing harmlessly, about one-and-a-half miles away.

It is only the fourth time in the 16-year history of the space station that a crew has had to rush into a Soyuz for protection from potentially dangerous debris.

Normally, Nasa learns about incoming junk sooner, and the space station moves out of the way.

But there was not time for that on this occasion; the crew was notified just 90 minutes in advance.