2009 DD45, estimated to be between 21 and 47 metres across, raced by at 1344 GMT (9.44pm Singapore time) on Monday, the Planetary Society and astronomers' blogs reported.

The gap was just 72,000 kilometres, or a fifth of the distance between Earth and the Moon and only twice the height of satellites in geosynchronous orbit, the website space.com said.

The estimated size is similar to that of an asteroid or comet that exploded above Tunguska, Siberia, on June 30 2008, flattening 80 million trees in a swathe of more than 2,000 square kilometres.

2009 DD45 was spotted last Saturday by astronomers at the Siding Spring Survey in Australia, and was verified by the International Astronomical Union's Minor Planet Centre (MPC), which catalogues Solar System rocks.

The closest flyby listed by the MPC is 2004 FU162, a small asteroid about six metres across which came within about 6,500 km of us in March 2004. -- AFP