NASA is closely monitoring an asteroid thought to be up to the size of Big Ben as it "skims" past the Earth later today.

The space rock, named 2016 JG38, after the year it was discovered, is classed by the US space agency as a "Near Earth Object" due the proximity of the pass to our planet.

Such objects are monitored by NASA to learn more about the asteroids and comets that pass us and, more importantly, because if its course changed it could potentially endanger the planet.

The asteroid is believed to be between 42 to 93 metres in length, based on observations, and will pass the planet at 4.12pm BST today.

If a space rock of such a size were to impact Earth, it could destroy a whole city, and lead to rapid climate change.

Fortunately, it is expected to pass by at just over three million miles away - or 13.17 times the distance between Earth and the Moon.

This is still considered a "close pass approach" by NASA in terms of the scale of the solar system.

Large numbers of "near Earth" asteroids pass the planet each month, with NASA keeping close tabs on them for very good reason.

A smaller asteroid called 2024 SN8, which was discovered this year, passed the Earth at about 7.30am today BST at a much closer distance of 771,000 miles away.

The rock, only discovered this year, is up to 40 metres in size, meaning a direct strike would be a significant event.

There are 38 further close approaches being monitored by NASA in October.

NASA has developed technology that can knock an asteroid off its path and it is hoped this could be used in the event of one that was actually on target to hit us, to ensure it passed safely instead.

The space agency trialled it in 2022 when its DART mission deliberately crashed into the Dimorphos asteroid to see if they could be diverted.

In September 2022, NASA's DART mission deliberately crashed a vending machine-sized space probe into the 151m-wide asteroid to see if it would be nudged enough to change its course.

Yesterday, the European Space Agency (ESA) sent its Hera spacecraft on a mission to the Dimorphos, 195 million kilometres away, to investigate the impact of NASA's test.

Hera, which is the size of a car, will also investigate a second asteroid during its mission.

Josef Aschbacher, director general of ESA, said: "The risk of an asteroid hitting our planet affects everyone everywhere, making planetary defence an inherently international endeavour."

Dimorphos is a moon of a larger asteroid, Didymos, the binary asteroid chosen as a target.

It was expected that the moon asteroid would remain in the bigger one's gravitational pull.

Early observations of the DART impact showed it changed Dimorphos's orbit around Didymos by around 32 minutes - 26 times greater than the minimum deflection predicted.

Hera will also set off two micro-satellites that will go into orbit around the asteroid system and then land on Dimorphos's surface, to get more information about its composition.

Mr Aschbacher added: "Hera will gather the data we need to turn kinetic impact into a well understood and repeatable technique on which all of us may rely on one day."

Earth has been hit suffered more than three million times by bits of space rock in our 4.5bn-year history.

The most significant was a 110-mile wide asteroid that hit at Chicxulub, Mexico, 66 million years ago, which wiped out the dinosaurs.