Mysterious bright lights have been spotted in the sky over Melbourne's western suburbs this morning.

Streaks of luminous blue, green and white lit up the area shortly before 6am.

The phenomenon was most likely caused by space junk or a meteor entering our atmosphere, according to Australasian Science Magazine astronomy expert David Reneke.

"My favourite (possibility) is always the fireball - that is, a meteor that's on fire," he said.

"It's pretty rare. I've seen two in my lifetime. You're seeing a piece of rock physically melting in front of your eyes. These things are pretty startling."

The lights probably moved too quickly for anyone to catch the event on camera, he said.

The spectacle comes after orbiting junk came perilously close to the International Space Station on Wednesday.