Asteroid alert: 12H countdown as NASA tracks an asteroid headed our way – Will it hit?

NASA’s astronomers believe any object below 82ft (25m) will disintegrate or explode before reaching the ground.

But at the upper end of NASA’s estimate, the asteroid is comparable in width to about four-and-a-half London doubledecker buses.

If the asteroid hits Earth, the impact could be catastrophic.

The Planetary Society said: “An asteroid of about 20 meters diameter like the one that exploded over Chelyabinsk, Russia, in 2013 on average will hit once or twice a century.

“Its shock wave shattered windows and injured more than 1000 people.”