An asteroid similar in size to an object that exploded above Siberia in 1908 with the force of 1,000 Second World War-era atomic bombs sped past the Earth on Monday, astronomers said Tuesday.

The asteroid, 2009 ND DD45, estimated at 21 to 47 metres across, passed 72,000 kilometres from the Earth at 8:34 a.m. ET, according to NASA's Near Earth Object program.

While 72,000 km may seem a fair distance, it is a fifth of the distance from the Earth to the Moon and about twice as far as the geosynchronous orbits of communications satellites.

The next closest approach of an asteroid in the past week was 2009 DT43, which was about half the size and passed about 390,000 km from Earth on Feb. 26.

The space rock was discovered only two days ago in the sky by Rob McNaught at Siding Spring Observatory in Australia, when it was "a dim speck about 1.5 million kilometres away," the U.S.-based Planetary Society wrote on Tuesday.

At the closest approach, it was over the Pacific Ocean near Tahiti. It could be observed from  Australia, Japan, and China, but not from North America or Europe, the Planetary Society said.

The asteroid's size is slightly smaller than the rock that exploded in the atmosphere at an altitude of six to 10 kilometres above the Tunguska region of Siberia in 1908.

That rock, estimated to be about 50 metres in length, sent a blast of heat and a shockwave with a likely energy equivalent of about 10 to 15 megatons of TNT, or about 1,000 times more powerful than the blast from the bomb dropped on Hiroshima during the Second World War.

An estimated 80 million trees covering more than 2,150 square kilometres were flattened, but only two deaths were reported in the sparsely populated region.

The closest listed approach to Earth was a small asteroid designated 2004 FU162, which passed within 6,500 kilometres, or roughly one Earth radius. It was about five to 10 metres in diameter.