An asteroid the size of a bus is set to fly past Earth in the coming hours.

The object, known as 2020 SW, will fly just 13,000 miles above the Earth's surface on 24 September, Nasa has said. That is closer than the artificial objects that are in orbit around our planet.

The object was only discovered on 18 September by a Nasa-funded project in Arizona, and further observations were able to track its trajectory and rule out any chance that it might collide with Earth. Those estimates showed that it would make its closest pass around noon UK time on Thursday.

It will then fly off to continue its trip around the solar system. It will not come back anywhere near Earth until 2041, when it will be at an even further distance.

The asteroid is thought to be about five to ten meters wide, roughly the size of a "small school bus", the space agency said. The size is estimated from the brightness of the object.

It is not expected to hit Earth. If it were, it would explode into a fireball as it made its way through the atmosphere, becoming a bright meteor of the kind that is sometimes visible from Earth's surface.

Despite repeated suggests that the world is under threat from such asteroids, their visits are fairly common and never pose any great risk to people on Earth.

"There are a large number of tiny asteroids like this one, and several of them approach our planet as close as this several times every year," said Paul Chodas, director of the Center for Near-Earth Object Studies (CNEOS) at NASA's Jet Propulsion Laboratory in Southern California. "In fact, asteroids of this size impact our atmosphere at an average rate of about once every year or two."

Experts have repeatedly suggested that asteroids more generally could pose more of a threat, and space agencies including NASA conduct "planetary defence" work intended to improve the chances of spotting an asteroid and dealing with any that might possible lead to any danger.

NASA has been tasked with finding 90 per cent of the near-Earth asteroids that are 140 meters or bigger. Such asteroids are far more dangerous than those akin to 2020 SW, since their larger size means they are able to make it through the atmosphere and potentially cause problems when they crash into Earth.

Their larger size also makes them easier to spot, however. There are many more smaller ones of sizes similar to 2020 SW, but their smaller size and lower brightness makes them difficult to see until they get close by.

"The detection capabilities of NASA's asteroid surveys are continually improving, and we should now expect to find asteroids of this size a couple days before they come near our planet," said Chodas.