Two asteroids are to zip close by Earth within hours of each other on Wednesday, the US space agency said.
The asteroids measuring several metres in diameter were discovered on Sunday by a telescope in Arizona and will pass closer than the moon's distance to Earth, NASA said. Though asteroid's come within that distance of Earth regularly, it is rare for two to do so in such a short period of time.
The first asteroid known as 2010 RX30 measures 10 to 20 metres and will pass within 248,000 km of Earth at 0951 GMT. The second known as 2010 RF12, measuring some 6 to 14 metres, will come just 79,000 km from Earth at 2212 GMT.
The objects should be visible from moderate strength amateur telescopes, NASA said.