Loud blast wakes Victorians as mysterious 'fireball' shoots across the sky

Tens of thousands of people across Victoria have been left in awe after a mysterious "fireball" catapulted across the sky overnight, leaving homes "shaking" and residents baffled.

The strange phenomenon occurred just before midnight, with people all the way from inner-city Melbourne to those living in the regions having reported witnessing the incredible event.

Footage uploaded to social media showed a kilometres-long bright object, akin to that of a shooting star, soaring across the night sky, leaving a trail of blue and silver in its wake.

What was the light in the sky?

Many hypothesised online on exactly what the bizarre sight was, with theories ranging from extra terrestrial activity to a potential meteor. Astronomer Alan Duffy confirmed to Yahoo News Australia it was most likely a large piece of space junk.

"The fireball indeed began to break up, and even the fragments themselves were visibly burning, all of that means it was something very large, perhaps a couple of tonnes," he said.

"The colours of those burning fragments changed, indicating large amounts of either plastics or metals, in other words this was artificial. This was space junk."

Mr Duffy said "we very much likely saw an upper stage of a rocket" re-entering the earth's atmosphere.

"Reports of large explosions — or sonic booms — means that the fragments reached low to the earth's surface at the very least," he said.

"That means they were very dense pieces, possibly a rocket's engine. Some of that might even have made it to land."

Object's origin a mystery

Usually, scientists have a "very good idea" which pieces of space debris are expected to enter the earth's atmosphere, however in this instance, there were no "usual suspects predicted for this period", meaning exactly where the object originated from remains a mystery.

Mr Duffy said by the end of the day experts should have a better idea of where it came from.

"It could've been from Russia," he said.

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"That's perhaps possible, but at this stage there's no confirmation out there and nobody's claimed it.

"Something this big, bright with this many witnesses, means that we'll be able to get enough data to get its trajectory down exactly and that will allow us to determine exactly what the object was and who to send any surviving pieces to."

Space junk unlikely to have come close to people

The junk poses very little danger to people, in fact the chances are "absolutely tiny" that anybody would ever be close to a landing piece of debris, he added, so "this one is safe to sit back and enjoy".

"The boom people heard means that the pieces were getting very close to the surface, perhaps a couple of kilometres from the ground," Mr Duffy said. "That's why I think it's perhaps possible that something landed."

Dozens of residents took to social media overnight to showcase their footage of the event.

Many claimed their homes were left "shaking" as the piece of debris shot over above. Others reported hearing "large booms".

"I live out in Wallan and felt my house shake and heard a bang," one user said.

"Didn't see it but heard it, sounded like someone smacked into the wall behind my head," said another.

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