Lucky skywatchers who spotted a rare daylight meteor streaking across the Victorian sky might never see one again in their lifetime, said one astronomer.

Reports of the burst of flame across the blue sky started flooding through on social media at about 10.30am on Wednesday, with one describing it as a "fireball asteroid".

Astronomical Society of Victoria spokesman Perry Vlahos said he had heard reports of the sighting across the state, from Mildura to Wangaratta to Melbourne.

"It appears to have come in from the western sky burning with a bright orange colour and leaving a white trail behind it," he said.

Mr Vlahos said the soaring fireball was probably a space rock that has been pulled in by the Earth's gravity and burned up in the atmosphere.

The flaming rock did not hit the ground, he said, meaning it was a meteor as opposed to a meteorite.

Spotting a daylight meteor is considered to be quite rare, due to the energy required to light up the sky when competing with the sun.

The main difference with night-time meteors, known widely as shooting stars, is the size. Mr Vlahos said a meteor visible at night could be as small as a grain of sand or an apple pip.

"For something to be seen during daylight hours, it's got to be a little bit larger than that. I'm suggesting it might be about the size of a walnut, up to the size of a cricket ball."

Mr Vlahos said this meant the skywatchers looking up at the right time on Wednesday were very lucky.

"It is very rare that they saw it. I would say those that did wouldn't see another one in their lifetime," he said.