An earthquake off North Wales early on Wednesday has been felt across an area more than 100km wide, the British Geological Survey (BGS) says.
The 3.8 magnitude quake had its epicentre in the Irish Sea 15km from Abersoch, Gwnedd, and was felt as far away as Southport in Merseyside, the Survey said.
The tremor at around 4.15 am sparked more than 100 reports from people who felt it, the majority within a 100km radius.
"This was a larger than average earthquake, we get around one a year of this size," the BGS said.
"Most people described having been awoken from their sleep by the moderate shaking strength of the earthquake, which had a trembling effect. Many of the reports stated that windows and crockery rattled," it added.
The organisation cited people as saying: "The bed was shaking, too scared to look at anything else", "Loud rumbling sound woke me, then noticed s sound of mirror rattling on bedside cabinet?, "Classic underground train passing sensation" and "woke the household any many neighbours."
There were also reports of the earthquake having been felt on the east coast of Ireland, the Survey said.
The largest ever British quake struck in the North Sea in 1931, with a magnitude of 6.1.
As the epicentre was 120 kilometres offshore it caused only minor damage to buildings on the eastern coast, but the tremors were felt as far away as Germany and Denmark.