An asteroid about the size of a bus shaved by Earth on Friday in what spacewatchers described as a "near-miss," though experts were not concerned about the possibility of an impact.
The asteroid, named 2012 BX34, measured between six and 19 meters in diameter, said Gareth Williams, associate director of the US-based Minor Planet Center which tracks space objects.
The asteroid, which had been unknown before it popped into view from a telescope in Arizona on Wednesday, came within about 60,000 kilometres of Earth on Friday at about 1500 GMT (0400 Saturday AEDT), he said.
"It's a near miss. It makes the top 20 list of closest approaches ever observed," Williams told AFP.
Nasa had announced on Twitter on Thursday that the asteroid would "safely pass Earth on January 27."
Williams explained that since the asteroid was so small, it could only be detected when it was close to the Earth, but that the fly-by, while a surprise, was not terribly uncommon.
"This came about a sixth of the distance from the Moon," he said. "In the past year we have had some 30 objects that were observed to come within the orbit of the Moon."