Some coastal towns in south-west Britain have been shaken by a 4.1-magnitude earthquake, experts said.
The British Geological Survey (BGS) said residents reported their houses rocking and others have described the quake as "frightening".
But others likened the tremor, which originated in the Bristol Channel at 13:21 today, to a "heavy truck going up the road".
Tremors were felt in areas including Dartmoor, Bristol, Taunton, Swansea, Llanelli, Barnstable, Gloucester and South Molton, the BGS said.
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A spokesman said: "At this time the BGS have received several macroseismic reports from residents throughout Devon and South Wales.
"One describing 'the house was rocking', another described 'lasted several seconds and it was very frightening' and another said 'it felt like a really heavy truck going up the road'."
Bay FM radio in Exmouth said the radio studios shook.
Twitter user Robin Beer said: "Anybody else feel the earth tremor just now?! #ndevon #barnstaple #earthquake."
Ant Veal tweeted: "Noticeable earth tremor just now (13.22GMT) in Exeter. Lasted 3 seconds. #Devon #earthquake."
Glenn Watts added: "Small tremor felt in Exeter, lasted 5 seconds armchairs wobbled as did the tv on its stand."
People in South Wales also reported feeling the ground shake.
Someone using the name @BuskingWomble wrote: "Blimey did anyone else feel that tremor? #BurryPort #Llanelli."
Another user said: "Earthquake Tremor in Wales today. We felt it in the building in Swansea."