The asteroid fly-by 'is the closest until at least the end of the next century', said Steve Ostro, a senior astronomer at the space agency NASA's Jet Propulsion Laboratory in Pasadena, California, in a statement.

'It is also the asteroid's closest Earth approach for more than 2,000 years,' he added, after the laboratory used high-resolution radar data to produce an image of the hulking asymmetrical object.

Roughly 250 metres in diameter, asteroid 2007 TU24 would inflict devastating regional damage were it to hit Earth, but Nasa said there is no risk of a collision.

It was due to pass within 538,000 kilometres of Earth just after 0830 GMT (4.30pm Singapore time).

'For a brief time the asteroid will be observable in dark and clear skies with amateur telescopes of 7.5 centimetres or larger,' NASA said earlier. -- AFP