Dr Ed Lu, a physicist and former NASA astronaut, said there is a 30 per cent chance that a near-Earth asteroid would hit the planet within this century. He estimated the hit would have a five-mega tonne impact.

Although Earth has technologies to prevent the impact on the planet, Mr Wu said that unless there are years of advance notice, there would be no options left.

Meanwhile, NASA Administrator Charles Bolden told the House Science, Space and Technology Committee on Tuesday that while there are 10,000 asteroids big enough to destroy a large city, there is an extremely remote chance any of them will hit Earth in the next hundred years.

He reported that in 1998, NASA found several hundreds of Near-Earth objects which had gone up to almost 10,000 by 2012. About 95 per cent were bigger than 0.62 miles across.

While 50 to 150 tonnes of space debris hit the Earth's atmosphere almost every day, most of it burns up before it reaches the ground, the NASA scientists said. Most of these are dust and small particles as large as small cars. They often crash and burn in the atmosphere once a week.

John Holdren, science adviser of the White House, said that Congress's directive for NASA to detect 90 per cent of these asteroids by 202 is much more challenging than detecting the larger objects.

"The odds of a near-Earth object strike causing massive casualties and instruction of infrastructure are very small, but the potential consequences of such an event are so large that it makes sense to take the risk seriously," Mr Holdren told the legislators.

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