A gigantic asteroid classified as "potentially hazardous" hurtled safely past Earth on Thursday night, zipping by well outside of the moon's orbit but nonetheless thrilling amateur stargazers.

The space rock, dubbed asteroid 2012 LZ1, was described by astronomers as being about 502 metres in width — roughly the size of a city block. As predicted, the flyby was about 5.3 million kilometres from Earth — equivalent to about 14 times the distance between the Earth and the moon.

But from home computer screens, where the public was able to watch a live feed of the celestial event, LZ1 appeared more like an oblong white dot rocketing past a backdrop speckled with stars.

A powerful telescope called the Slooh Space Camera tracked and broadcast views of the newly discovered near-Earth asteroid from an observatory at the Canary Islands, off the west coast of Africa.

Although scientists said the asteroid never posed much of an impact threat, Patrick Paolucci, president of the Slooh Space Camera, said it should still be considered a close brush in astronomical terms.

"It's relatively big and it's pretty close. We talk about distances — 14 moon distances might [seem] pretty far away, but actually it's pretty close," he said in Thursday night's webcast.

'Dodging bullets'

Astronomy Magazine analyst Bob Berman added during the webcast that the event was "scary" and a bit of a wake-up call for astronomers, who only discovered the LZ1 this week.

"The word space certainly means there's room up there, but now it's almost like we're dodging bullets here and there," he said. "We thought things like this size, we'd easily detect more than just a few days before they zoom past us. This one is a little bit worse that we could see something the size of a city block and not detect it until just three days beforehand."

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This NASA radar image showing asteroid 2005 YU55 was obtained in 2011. The asteroid, said to be about the size of an aircraft carrier, came within 325,000 kilometres of Earth. (NASA)

Berman said LZ1 was whizzing through the night sky at speeds of about 16 kilometres per second.

Near-Earth asteroids are not an uncommon occurrence. Astronomers have recorded roughly 9,000 of them to date, according to the astonomy news website Space.com.

Last month, an asteroid about the size of a school bus called 2012 JU cruised by within 191,500 kilometres of our planet. In November, the aircraft carrier-sized 2005 YU55 came within 325,000 kilometres of Earth before continuing on its way into the cosmos. That asteroid was within the orbit of the moon.

Berman said the next significant close encounter with another near-Earth asteroid of a magnitude similar to LZ1's will be with the 99942 Apophis, forecast to come on an ominous date — Friday, April 13, 2029.

"That will come so close it's going to pass between us and our TV satellites. That'll be bright enough to see easily with the naked eye," Berman said.

Depending on how much the Earth's gravity shifts six years after that, there is a small probability — about a one in a 250,000 chance — that an impact may occur when Apophis swings through again.

"Not anything to worry about," Berman said.