The asteroid, estimated to be about 11m (36ft) in diameter, was first detected on Wednesday.
At its closest, the space rock - named 2012 BX34 - will pass within about 60,000km of Earth - less than a fifth of the distance to the Moon.
Astronomers stress that there is no cause for concern.
"It's one of the closest approaches recorded," said Gareth Williams, associate director of the US-based Minor Planet Center.
"It makes it in to the top 20 closest approaches, but it's sufficiently far away... that there's absolutely no chance of it hitting us," he told the BBC.
The asteroid's path makes it the closest space-rock to pass by the Earth since object 2011 MD in June 2011. Read More