Homes across the East of England were shaken as the biggest earthquake for nearly 25 years hit the UK.
The earthquake had a magnitude of 5.2, experts said
Police in Norfolk, Cambridgeshire and Northamptonshire received hundreds of calls after tremors were felt just before 0100 GMT.
The epicentre of the magnitude 5.2 quake was in Market Rasen, Lincs, but it was felt in much of England.
The British Geological Society said an earthquake on this scale would occur about every 10 to 20 years in the UK.
No injuries or damage have been reported across the East, but people were woken in their beds by the earthquake.
Robin Johnson, of Corby, Northamptonshire, told the BBC: "At first I thought there was an enormous animal on the roof though I knew what was actually happening when the whole room began to shake."
In Milton Keynes, Matt Lawson said his house shook for about five seconds.
He said: "It was like a giant was shaking my house! A very surreal sensation."
Barry Leslie, of Market Deeping, Lincolnshire, said: "The whole house was shaking and it felt as if the house was made of rubber.
"The most disturbing thing was the horrendous high-pitched vibration that accompanied it."
Sarah Lester, of Cratfield, Suffolk, said her house shook for a few seconds and she was left "trying to coax an alarmed cat out of the wardrobe".
Insp Phil Kings, of Northamptonshire Police, said the force received about 250 calls from all parts of the county, particularly Northampton, in relation to the tremor in the half hour following it.
Cambridgeshire Constabulary control room received 41 emergency 999 calls and almost 200 non-emergency calls from residents concerned by the earthquake over the same period.
Norfolk Police received about 180 calls from county residents about the tremor.
Police in Suffolk and Essex said they received calls about buildings "shaken" by the tremor but there were no reports of any damage or casualties.
The main 10-second quake struck at 0056 GMT and was the biggest recorded in the UK since one measuring 5.4 on the Richter scale hit north Wales in 1984.