NASA scientists say a massive asteroid now has no chance of hitting earth in 23 years time after revising calculations.

The Apophis asteroid, which is around the size of almost four rugby fields, had been given a 2.7 per cent chance of striking the earth during a close fly-by on April 13 2036.

But, after the asteroid whizzed past earth earlier this week, they were able to recalculate and now make it less than a one-in-a-million shot.

“With the new data provided by the Magdalena Ridge [New Mexico Institute of Mining and Technology] and the Pan-STARRS [Univ. of Hawaii] optical observatories, along with very recent data provided by the Goldstone Solar System Radar, we have effectively ruled out the possibility of an Earth impact by Apophis in 2036,” said Don Yeomans, manager of NASA's Near-Earth Object Program Office at JPL.

“The impact odds as they stand now are less than one in a million, which makes us comfortable saying we can effectively rule out an Earth impact in 2036.

“Our interest in asteroid Apophis will essentially be for its scientific interest for the foreseeable future.”

At over 300 metres wide, the damage caused by a collision with an asteroid of this size would have been devastating, but not an extinction event.

However, this asteroid will become the closest object of that size to fly past the earth, when it whizzes past at just 31,300 kilometres above the earth’s surface.

While Mr Yeomans added: “A closer approach by a lesser-known asteroid is going to occur in the middle of next month when a 40-metre-sized asteroid, 2012 DA14, flies safely past Earth's surface at about 17,200 miles.”