Three nights of skywatching by an Australian astronomer have confirmed predictions that an asteroid almost half-a-kilometre wide will miss the Earth on Monday by 430,000 kilometres.

However, it would still be "one of the largest objects to be observed to pass this close to the earth", said Rob McNaught, an astronomer at Siding Spring, near Coonabarabran.

If the predictions had been wrong, and the asteroid, dubbed 2004 XP14, hit the Earth, "you would be talking about very serious consequences", he said. The astronomer and his colleague, Gordon Garradd, run the southern hemisphere's only search for asteroids that pose a threat to life on earth.