Everyone in the south-west yesterday had their own big bang theory.

Was it an earthquake? Did Tower Hill erupt into action? Did a meteor shower crash to earth, or was it an alien invasion?

The "big bang" was heard about 1am yesterday, with reports of an "explosion" shaking homes in Winslow, Warrnambool and Terang.

"The whole house shook and there was an almighty noise, like a roar," one Warrnambool resident said yesterday.

"It had my curtains moving and set my car alarm off."

The noise was said to be accompanied by flashes of light that were variously described as being pink, orange and yellow, and seen as far away as Mortlake and Heywood.

Perry Vlahos, media liaison for the Astronomical Society of Victoria (ASV), said it was likely that the bang and the flashes of light were caused by a meteor.

"It was most likely a meteor exploding in the atmosphere," Mr Vlahos said.

"(The sound) could be a sonic boom or (a meteor) coming through the atmosphere and exploding. Even though these flashes or sound appear close, it might be quite a distance above our head."

Don Ward, an ASV member from Gorae West, said the cloudy conditions would have made it difficult to spot a meteor.

"But this talk of lights suggests it might have been an explosion above the cloud level and it illuminated the clouds," Mr Ward said.

"(As for the bang), you would get that as the meteor reached a certain level and the air resistance and friction results in disintegration. Then if it falls to earth in pieces, that is what we call a meteorite."

Mr Ward said a lack of meteorite pieces or a smoking crater did not invalidate the theory, as the meteor could have turned to ashes, or they could have gone into the sea.

The Standard confirmed that it wasn't an earth tremor, with Geoscience Australia reporting that no seismic activity had been recorded in the region.

In the absence of a definitive answer - and without any reports of damage - rumours, pranksters and conspiracy theorists began swirling early yesterday.

A tsunami was heading towards Lady Bay, an earthquake recording 5.3 on the Richter Scale caused "extensive minor damage" and a passing defence force plane had created a sonic boom.

Some seriously questioned if it was alien life or a sign pointing towards a looming apocalypse.

On The Standard's online poll, which had attracted more than 1100 responses last night, more than half thought the "big bang" was from visiting extraterrestrials.