NASA says two small asteroids discovered just days ago will zip harmlessly past Earth on Wednesday, a double flyby that should be visible through a telescope.

The asteroids were discovered on Sunday by the NASA-funded Catalina Sky Survey in Arizona.

The Minor Planet Center in Massachusetts, which tracks asteroids and comets, determined there was no chance of an Earth collision.

Asteroid 2010 RX30, thought to be 10 to 20 metres long, will pass within 248,000km of Earth shortly before 2000 AEST on Wednesday.

The second one, dubbed 2010 RF12, will fly by about 11 hours later at a distance of about 79,000km.

NASA says the second one is 6 to 14 metres long.