An asteroid about half a football field in diameter will hurtle just 28,000 kilometres past Earth next week.
Details of the ancient asteroid, named 2012 DA14, are sketchy, the European Space Agency says.
From its brightness, scientists estimate its diameter to be between 50m and 80m. Its composition is unknown and its mass is thought to be about 130,000 tonnes.
Detlef Koschny, responsible for near-Earth objects at European Space Agency's Space Situational Awareness office, said the orbit of the asteroid can be computed "quite accurately".
"These computations show that a collision with Earth can be excluded quite safely at least for this century," Koschny says.