A small asteroid was headed for a fiery but harmless dive into Earth's atmosphere early Tuesday morning over Africa, astronomers said in a first-of-its-kind advance notice.

Harvard scientists announced late Monday afternoon that the asteroid 2008 TC3 would burn up in the sky, making a fireball potentially visible to people in northern Africa. Measuring between one metre and five metres in diameter, the rock was expected to enter Earth's atmosphere above Sudan at 10:46 p.m. EDT Monday, just before dawn in Africa.

Harvard astronomer Tim Spahr said the asteroid was so small it wouldn't reach the ground before burning up and wouldn't hurt anyone, but the fireball should be seen heading from west to east.

"It's the first time we've been able to predict an impactor in advance and it'll be quite a celestial show for the world," said Donald Yeomans, manager of NASA's Near Earth Object program, which tracks asteroids and comets that come close.

There are 5,681 such objects, but only 757 of them are large enough to cause any damage if they hit Earth.

This object, spotted by an Arizona telescope late Sunday and calculated on Monday to be heading toward Earth, isn't dangerous. Astronomers don't know precisely how big it is or what it is made of, but they know that it is small enough that it will burn up. As it enters the atmosphere, becoming a meteor, it compresses the air in front of it, which then gets hotter, causing a fireworks display.

Rocks this size hit Earth's atmosphere about two or three times a year, but usually without warning, Yeomans said.

Astronomers were only able to give the world about six hours notice because the rock is so dark and small. It was spotted a little farther away from Earth than the moon, said Spahr, director of the International Astronomical Union's Minor Planet Center.

Astronomers hope by scanning the sky they can eventually give Earth warning of more worrisome rocks that come this way.

"If this were something larger and it was going to hit the ground, we would be able to get people out of the way," Spahr said. But with something this size, they can tell people to look up for a sight that could be "pretty cool from the ground," he said.