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A "potentially hazardous" asteroid the size of a sports stadium will zoom past Earth in the coming days, NASA said.
The space agency says Asteroid 2008 OS7 is expected to come within 2.8 million kilometres of Earth – about seven times further from our planet than the Moon.
Scientists will be keeping a close eye on the giant space rock that is about 270 metres in size.
READ MORE: Warning over 'massive damage' to moon as new space race begins
Despite the vast distance from Earth, it is close enough in astronomical terms for it to be put on NASA's "asteroid watch" list.
That means in the event of an impact it would cause significant damage.
It is expected to make its closest approach to Earth about 1.40am (AEDT) on Saturday.
Minjae Kim, a space expert at Britain's University of Warwick, said research showed 2008 OS7 was a small to moderately sized asteroid, "roughly equivalent to the size of a football field."
He said NASA was erring on the side of caution in its warning.
"We don't need to worry about it too much as this asteroid will not enter Earth's atmosphere, while it will still approach close to the Earth.
"There are millions of asteroids in our solar system, of which around 2,350 asteroids have been classified as potentially hazardous."
Most asteroids and comets do not pass very close to Earth. They are only classed as dangerous if they come within 7.4 million kilometres and are larger than 140 metres.
