Thousands of people reported the tremor, with its epicentre falling around eight miles northeast of Swansea city centre, close to the village of Clydach, according to the British Geological Survey (BGS).
The quake was felt across South-west England, with residents in Bristol and Cornwall reporting the phenomenon, and as far away as Carisbrooke Castle on the Isle of Wight, more than 125 miles away.
Alison Morgan, who works at Uplands Newsagents in Swansea, said: “My colleague noticed it first and wine bottles in the shop were shaking and a tile fell off the ceiling.
“I thought it was a lorry going past but it was an earth tremor.
“It was a significant feeling that went on for about two seconds – I was moving from left to right suddenly despite being stood on the same spot.”
In Bristol, there were several reports of buildings being damaged by the tremor.
Avon Fire and Rescue Service said it has received at least six calls relating to damage to properties and attended two incidents to make sure buildings were safe.
A brigade spokesperson said: “We have had a half a dozen calls to report the earthquake. We have responded to one in the Bristol area to give advice after concerns about structural damage.
“We attended the home in the Knowle area and made checks and couldn’t find any damage.
“We would encourage anyone with similar concerns, particularly if they have issues with subsidence, to contact a structural engineer or their landlord.”
Animals were said to be among the first to sense the movement. Donna Johnson, from Caerphilly, told the BBC: "I ran outside - I was shaking like a leaf... The cat went outside before me, so she must have known."
Vera Sanderberg, from Croyde in north Devon, said: "The neighbour's horses bolted."
Twitter users reported feeling the quake as far away as Gloucestershire.
“Felt that #earthquake in Etloe, 80 miles from Swansea”, Simon Evans wrote. “Thought the house was about to fall down.”
Felt that #earthquake in Etloe, 80 miles from Swansea. Thought the house was about to fall down.— Simon Evans (@siiimon) 17 February 2018
Lianne Watson, who works at the Village Tavern pub in Clydach, said the 20 staff and customers in the building at the time had felt the quake.
“We felt it here,” she told The Independent: “I just thought someone had slammed a door outside to be honest.”
The BGS said on Twitter it was in the process of analysing data from the quake and would provide more information soon.
We are in the process of analysing data for the felt report of a tremor in the SW of England. As soon as we know more we’ll let you know.— BGS (@BritGeoSurvey) 17 February 2018
Swansea University, which was holding an open day, saw its Bay Campus evacuated as a result of the tremor.
Parent, Dermot Martin, said: “My son who is at Uni in Swansea said he was in the loo at Bay Campus when the walls started shaking for about six seconds.”
South Wales Police said it had received a high number of calls to report the quake.
A police spokesman said: “There has been a minor earthquake throughout South Wales.
“No need for you to contact the emergency services unless you have something to report such as injuries or damage.”
According to the BGS, more than 300 earthquakes are recorded on the UK mainland each year.
However, earthquakes of magnitude four or higher are a relatively rare occurrence, taking place on average once every two years.