A huge asteroid will pass closer to Earth than the moon this week, but scientists say there is no chance of a collision.

Earth's close encounter with Asteroid 2005 YU55 will occur at 10:28am (AEDT) on Wednesday, as the space rock sails about 323,469 km from the planet.

"It is the first time since 1976 that an object of this size has passed this closely to the Earth," astronomer Scott Fisher, a program director with the National Science Foundation, said.
"It gives us a great and rare chance to study a near-Earth object like this."

The orbit and position of the asteroid, which is about 400 metres in diameter, is well known, added senior research scientist Don Yeomans from NASA's Jet Propulsion Laboratory in Pasadena, California.

"There is no chance that this object will collide with the Earth or moon," Mr Yeomans said.

Thousands of amateur and professional astronomers are expected to track YU55's approach, which will be visible from the northern hemisphere.

It will be too dim to be seen with the naked eye, however, and it will be moving too fast for viewing by the Hubble Space Telescope.

"The best time to observe it would be in the early evening on November 8 from the east coast of the United States," Mr Yeomans said.

"It is going to be very faint, even at its closest approach. You will need a decent-sized telescope to be able to actually see the object as it flies by."