The earthquake was recorded by the British Geological Survey
Residents on Shetland have been shaken by the effects of an earthquake.
Seismologists are investigating and the British Geological Survey (BGS) said "seismic activity" had been recorded on the island around 0530 GMT on Thursday.
Northern Constabulary said it had received calls from residents reporting a bang and their houses shaking.
A BGS spokesperson said the earthquake had a magnitude of 3.3, and was the largest to strike the area since October 2002.
The BGS said: "Reports described 'similar feeling to being moved forward then stopping with a jolt', 'windows shook, like as if a truck was driving past really fast and close', 'the noise got louder, then stopped, then the windows went in and out', 'growing rumble, sounded very much like a fast and very large train approaching', and 'like a loud explosion'.
"The strength of the shaking has been described in most cases as moderate, enough to make furniture shake and windows or crockery rattle. Some reports indicate that people were woken from sleep and a few were frightened."
A Northern Constabulary spokesman said: "We received a number of reports around 0535 GMT from residents in the Tingwall and Mossbank areas of Shetland.
"They reported hearing a bang and their houses shaking. We have no reports of any damage or injury."
Gordon Williamson, owner of the Herrislea House Hotel in Tingwall, said: "I woke with the building shaking and thought it was an explosion. We've just had a new boiler installed and I thought it was kaput, but when I went downstairs to check, it was fine.
Northern Constabulary said Tingwall was one area affected
"My wife thought something could have hit the building, so I went outside and walked around, but there was nothing.
"It was only a few hours later we found out it was an earthquake. You hear about these earthquakes on the news every now and again. We definitely felt this one."
Shetland Coastguard watch manager David Phillips added: "I was sitting at work early this morning when the building shook momentarily.
"We then got phone calls from members of the public who were concerned because they had heard banging and shaking.
"We have had no reports of any aircraft emergency or anything unusual happening. We are presuming it was an earthquake."