Experts are calling for the US to 'bolster' the defence against the threat of asteroids to prevent catastrophe.

As Politico reports, NASA believes the likelihood of a massive asteroid hitting Earth is a 'once in a millennium type of event'.

However, the space agency is also preparing to strike an asteroid with a spacecraft travelling at 16,000 miles an hour in a bid to move it off course - a year-long mission set to begin on 24 November.

It is using new telescopes and other technology to track down thousands of undiscovered near-Earth objects each yeah, with more than 27,000 located so far.

One such object, discovered this year in September, was the size of the Pyramid of Giza and flew by Earth at a distance of two million miles - something that's considered as a near miss in asteroid terms.

Former Air Force space strategist Peter Garretson, who studies planetary defense, told Politico that 'no one is tasked with mitigation' when it comes to asteroid defence.

He said: "Congress did put in law that the White House identify who should be responsible, but fully four subsequent administrations so far have blown off their request."

Senator Gary Peters, a member of the Armed Services and Commerce committees, said an asteroid strike is among the 'unique threats to national security', and is a leading advocate for greater preparations.

He told the outlet that the possibility of such a cataclysmic event demands that the US government does more to 'bolster federal planetary defense efforts'.

Danica Remy, president of the B612 Foundation, which is building a database to track near-Earth objects, added: "There are three million asteroids and we have not a freaking clue where they are and they are flying around us.

"We've barely made a dent."

The warnings come as NASA plans its first ever planetary defence test, known as the Double Asteroid Redirection Test (DART).

The mission will aim to change the trajectory of the asteroid Dimorphos, which orbits the larger Didymos.

"DART is a spacecraft designed to impact an asteroid as a test of technology," NASA says on its website.

"DART's target asteroid is NOT a threat to Earth. This asteroid system is a perfect testing ground to see if intentionally crashing a spacecraft into an asteroid is an effective way to change its course, should an Earth-threatening asteroid be discovered in the future.

"While no known asteroid larger than 140 meters in size has a significant chance to hit Earth for the next 100 years, only about 40 percent of those asteroids have been found as of October 2021."