Doomsday asteroid passing Earth

A 325m-wide asteroid that has a chance of smashing into Earth in 2036 is passing by today.

The Apophis asteroid , known as the "doomsday asteroid", was first predicted to have a one in 45 chance of hitting Earth in 2029.

Further studies have since dispelled the prediction, showing that it will pass Earth at a distance of 30,000km.

However, astronomers say there is still a one in 200,000 chance the rock could hit in 2036.

While today's passing will be at a safe distance of 14 million km, it is still close enough to study the asteroid and assess future risk.

Apophis' journey won't be visible to the naked eye, but star gazers can follow it on an online space camera which will stream views from telescopes in Italy and the Canary Islands beginning at 1pm (NZT).

Recent images of the asteroid captured by European Space Agency officials show that Apophis is nearly 20 per cent larger than originally thought, at 325m wide rather than the 270m diametre first reported.

"The 20 per cent increase in diametre ... translates into a 75 per cent increase in our estimates of the asteroid's volume or mass," said Thomas Mller of the Max Planck Institute for Extraterrestrial Physics in a statement.

UK astronomer Professor Alan Fitzsimmons told the BBC that the asteroid's 2029 passing will be so close that the Earth's gravity will change its orbit.

"Most of the potential orbits it will end up on will mean we are safe for the next 100 years. But there is a small region of space - something we call a keyhole - and if it passes through that keyhole in 2029, it will come back and hit us on 13 April in 2036," he said.

Should this happen, Apophis would hit the Earth's surface with 100 times the force of a nuclear bomb, Professor Fitzsimmons said.