An asteroid measuring about 30m across has zipped past the Earth, just 60,000km from its surface and inside the moon's orbit.
Australian National University astronomer Rob McNaught discovered the rock during a routine survey of asteroids passing close to the Earth.
Mr McNaught said this asteroid was the closest observed approach of an object of this size or larger.
''We find about 70 near-Earth asteroids every year and this is the closest approach asteroid [of this size] we've ever found, so that was a surprise,'' he said.
The asteroid, dubbed 2009 DD45, passed closest to the Earth at 12.30am on Tuesday.
An astronomy enthusiast captured footage of the asteroid's journey and posted it on the video sharing website, YouTube. Since it went up on Tuesday, the footage has received about 50,000 hits.
Mr McNaught said there was no chance the asteroid would have hit the Earth.
''Every year and a half or so it will be back,'' he said.
''But we know for the next hundred years, this object won't collide with the Earth.''
Other objects have the potential to hit the Earth, including the asteroid called Apophis, which has an outside chance of hitting in 2036. But MrMcNaught said the probability of impact was about 1 in 5000.
Mr McNaught studies the sky as part of the Spaceguard program, an international search for asteroids that may collide with the Earth.
He works with a team at the ANU's Siding Spring Observatory, often from dusk to dawn, examining images taken with a digital camera on a telescope. The team takes images of a patch of sky over about an hour and compares them to see if objects are moving.
Mr McNaught said he ''absolutely loved'' his job.
''I don't know why. Ever since I was a kid I enjoyed looking at the sky and finding new things,'' he said.