Mystery still surrounds the huge "explosion" reportedly heard across South Yorkshire this morning.
Dozens of people claim to have heard a huge bang in the Meadowhall area at around 5.15am - and numerous theories have been put forward as to what could have caused the noise which was heard more than 30 miles away.
READ MORE: Early morning "massive bang" reported at Meadowhall
Meadowhall "explosion" is heard 30 miles away
Here's five things that might have been responsible for the blast which woke people across the region and beyond this morning.
1. THUNDER AND LIGHTNING
South Yorkshire experienced some freak weather conditions yesterday - with thunderstorms, lightning, hail and snow all reported in Doncaster in the space of a few hours during the afternoon. The unique mix could have been an echoing thunderbolt.
The noise of exploding fireworks can sometimes carry remarkable distances - particularly if the atmospherics are right. However, the time the noise was heard - around 5am - suggest that it wouldn't have been someone holding a celebration.
3. AIRCRAFT SONIC BOOM
A sonic boom is a good contender - the sound comes from the shock waves created by an object traveling through the air faster than the speed of sound. Military, rather than civilian aircraft are generally responsible - and secret air force manoeuvres have been suggested as an explanation.
4. SINKHOLE/GROUND COLLAPSE
Earlier this week, a huge sinkhole opened up on Hutcliffe Wood Road - and the cause of the collapse was put down to old mine workings. More shifts and subsidence could have been responsible for this morning's rumblings.
5. INDUSTRIAL NOISE
Several readers suggested the noise could have been caused by a local firm, Heavy engineering works such as Forgemasters and steel companies use extremely heavy and powerful machinery and previous mystery noises have been attributed to bumps and bangs eminating from factories.