Space enthusiasts should have their telescopes and binoculars at the ready for the chance to spot a record-breaking asteroid tomorrow.

The piece of space rock, about 50 metres wide and called 2012 DA 14, was discovered in February last year.

It is approaching Earth in an orbit that will put it about 27,000 kilometres above us.

That will be the closest any object of its size has come to Earth, and consequently many astronomers would be setting their alarm clocks early to see it, Carter Observatory programmes manager John Field said.

Unfortunately, it would be at its brightest during daytime tomorrow morning, but would be visible from 2am to sunrise through a telescope or a good pair of binoculars.

"It's pretty rare to see these, but now that we have better telescopes and more people hunting we're getting more reports than ever before.

"Ten years ago, none of our telescopes could even spot them," he said.

He pointed out that there was no danger of it coming close enough to Earth to have any effect.

However, if an object of its size, travelling at up to 40,000km a second, entered the Earth's atmosphere, it would start to break up, releasing the force of about 3.6 megatonnes of TNT, the equivalent of 720 Hiroshima atomic bombs, Mr Field said.

"Put it this way, if that happened over our heads on Saturday, we wouldn't be here on the 17th.

"But the chances of that are slim, so we can all breathe a sigh of relief."

Those wanting to track the meteor are best to refer to the website Heavens-above.com.

NIGHT WATCH

Look for the asteroid in the east to southeast from about 2.30am tomorrow.

It will move across the sky from the south and disappear from view in the west about sunrise.

- © Fairfax NZ News