(CNN) A 4.4 magnitude earthquake shook Wales on Saturday afternoon, according to the British Geological Survey.

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The agency said on Twitter that the earthquake's epicenter was about 20 kilometers (12 miles) north-northeast of Swansea, Wales. It jolted the area at 2:31 p.m. local time (9:31 a.m. ET), it said.

The strength of the earthquake was particularly unusual for the region, the British Geological Survey said, adding that "events as large as this only happen every 3-5 years in the UK."

There were no immediate reports of major damage.

Saturday's earthquake was the biggest "onshore UK event" in 10 years, and the biggest in the area since a 5.2 magnitude earthquake in 1906, the British Geological Survey said.