Nasa says asteroid three times as big as Empire State Building is just a MONTH away from Earth ‘close approach’

NASA is keeping its eye on a gigantic asteroid that's just over a month away from a close approach with Earth.

The 'potentially hazardous' space rock is said to be up to 4,265 feet wide.

That makes it almost three times as big as the Empire State Building.

The Empire State Building stands at around 1,453 feet tall so would pale in comparison to Asteroid 138971 (2001 CB21).

Nasa has put the asteroid on its 'Earth Close Approaches' list.

The good news is it's not expected to hit Earth.

An asteroid of this size would do some serious damage.

It should shoot past us on March 4 from an estimated distance of 3million miles away.

In comparison, the Moon is only about 238,900 miles from us.

A few million miles may sound pretty far away but it's actually quite close in terms of space.

Nasa considers anything passing near Earth's orbit a Near-Earth Object (NEO).

Thousands of NEOs are tracked by scientists to monitor whether they're on a collision course with our planet.

Any fast-moving space object that comes within 4.65 million miles is considered to be "potentially hazardous" by cautious space organizations.

One small change to their trajectories could spell disaster for Earth.

Nasa thinks Asteroid 138971 (2001 CB21) will speed past Earth at around 27,000 miles per hour in the early hours of March 4.

That means the space agency has got just over a month to prepare for the flypast.

Plans to save Earth from asteroids

Some experts are worried that Earth isn't yet ready to defend itself from potentially deadly asteroids.

SpaceX CEO Elon Musk once sparked concern by tweeting: "a big rock will hit Earth eventually & we currently have no defence."