A huge asteroid that astronomers compared to the size of a city block will reportedly zip by so close to Earth tonight that skygazers should be able to witness it live on the web.

The giant space rock, dubbed 2012 LZ1, is roughly 502 metres wide, and will come within 14 "lunar distances" — a measurement of the distance from the Earth to the moon — from our planet.

At such a distance, the team running the high-powered Slooh Space Camera telescope predicts the asteroid will be visible on a live online feed from the Canary Islands. The broadcast of the flyby will be available on Slooh's website starting at 8 p.m. ET, though it won't be detectable by the naked eye.

The celestial event only caught the attention of astronomers days ago, when scientists peered through a telescope and noticed the giant asteroid's flight path, astronomy news website Space.com reported.

Due to its size and proximity to Earth, 2012 LZ1 qualifies as a "potentially hazardous" near-Earth asteroid.

While the 2012 LZ1 will likely come within 5.4 million kilometres of Earth, our planet is not in danger of being struck and asteroid flybys are not an uncommon occurrence.

Last month, for example, the 2012 JU asteroid gave us a closer shave, coming within 191,500 kilometres to our planet. That asteroid was described as about 12 metres wide, or about the size of a school bus.

Back in November, the massive 2005 YU55 asteroid also came within an astronomical whisker of impact with Earth, zooming past about 325,000 kilometres away, and just inside the moon's orbit. That asteroid was described as the size of an aircraft carrier, and was noted as the closest asteroid flyby in 30 years.