An asteroid the size of a large house will zip within 8,000 miles of Earth at about midday on Monday.
That's at least double the size of the asteroids that have previously been observed so close to Earth.
Called 2011 MD, the asteroid was discovered late on Wednesday by an automated asteroid-hunting telescope run by the MIT Lincoln Laboratory's LINEAR programme, which has already discovered more than 2,000 near-Earth objects. Within 24 hours, four other groups confirmed the discovery, according to the New Scientist website.
Heading our way: The asteroid is estimated to be up to 55ft high
The Minor Planet Center at Harvard University does not rate 2011 MD as potentially hazardous because its size - calculated from its brightness - is estimated to be betweein 24ft and 55ft. That would make an impressive explosion if it hit the atmosphere, but it wouldn't reach the ground.
On its current pass, 2011 MD won't hit Earth's atmosphere. It will come inside the orbits of many communications and spy satellites, but will still be some 7,750 miles away from the International Space Station. However, Spaceweather.com reports that the encounter is close for Earth's gravity to 'sharply alter the asteroid's trajectory'.
Discoveries of small near-Earth asteroids have soared since the year 2000 with the growth of automated sky surveys following in the footsteps of LINEAR, which found its first asteroid in 1996.
Statistics compiled by Nasa's Jet Propulsion Laboratory in Pasadena, California, show more than 8,000 known asteroids in near-Earth orbits. More than 7,000 of these are smaller than a mile across and almost 1,000 are smaller than 100ft.