A newly discovered asteroid the size of a city block will zoom past Earth but poses no risk of a collision, astronomers said on Thursday.

The "unusually large" asteroid will not be visible to the naked eye, but asteroid enthusiasts may watch it pass by during a live online broadcast, said Patrick Paolucci, president of the skywatchers' site Slooh.

NASA has already catalogued 9,000 such Near-Earth Objects, but astronomers are always on the lookout for new ones.

"Once in awhile one will come out of nowhere like this one, which is actually pretty big," Paolucci told AFP.

"We were like, 'Wow, we should track this one.'"

The asteroid, named 2012 LZ1, is thought to be about 500 meters (1,650 feet) wide, and is expected to pass within 14 times the Moon's distance from the Earth.

The massive object was discovered just days ago by Scottish-Australian astronomer Rob McNaught and colleagues at the Research School of Astronomy and Astrophysics of the Australian National University.

The asteroid qualifies as a Near-Earth Object because of its size and proximity -- more than 500 feet (152 meters) wide and within a distance of 4.65 million miles (7.5 million kilometers) from Earth.

Paolucci said the asteroid's fly-by would be covered in real-time with footage from an observatory in the Canary Islands at Slooh.com beginning at 8 pm (0000 GMT on Friday).