It is held on the anniversary of the Tunguska event in 1908, when an asteroid levelled about 2,150 square kilometres (830 sq mi) forest in Siberia, Russia.
Asteroid Day was co-founded by Stephen Hawking.
In December 2016, the United Nations General Assembly adopted a resolution to celebrate this.
The decision was made based on a proposal by the Association of Space Explorers, which was endorsed by Committee on the Peaceful Uses of Outer Space (COPUOS).
The theme of this year's event is "small is beautiful".