Fracking has been halted at Cuadrilla’s gas exploration site in Lancashire after tremors were detected underground.
The British Geological Survey recorded a 0.8 magnitude earthquake in the region of the site at about 11.30am on Friday.
It is the largest tremor at the Preston New Road, Little Plumpton, site since fracking began this month.
As a result of the “red event”, Cuadrilla has paused fracking operations for at least the next 18 hours as monitoring continues.
But the exploration company said “micro seismic” events like this do not cause any damage and cannot be felt at ground level.
“Events such as these result in tiny movements that are way below anything that would be felt at surface, much less cause any harm or damage,” a spokesman said.
The quake, which took place 2km underground, was classed as a red event under the UK’s fracking regulation traffic-light scheme, meaning it was more than 0.5M.
Read more: Fracking caused 2017 earthquake, study finds
Cuadrilla was hydraulically fracturing the shale rock adjacent to a well when the seismic activity was recorded, the spokesman said.
“All the relevant regulators were informed without delay and we have verified that the well integrity is intact,” he said.
The controversial fracking work began 11 days ago after an environmental campaigner failed in a High Court bid to block it.
The exploration is the first fracking in the UK for seven years, after work by Cuadrilla was halted in 2011 following two tremors near Blackpool.
Friends of the Earth campaigner Rose Dickinson said fracking poses risks to the environment and the latest tremor was “deeply concerning”.
“Fracking only started 11 days ago. In that time there have been 17 earthquakes, including one today that has reached a red warning level,” she said.
“This is deeply concerning for those living nearby and why the industry must be closely monitored.
“When is the Government going to realise that fracking is the wrong choice for Lancashire, the UK and our global climate?”
Friends of the Earth has helped to organise a petition, signed by some 300,000 people, to stop the fracking through the planning system.
A spokesman for BGS said Friday’s quake was recorded “right on top” of the Cauudrilla site and was the largest of 17 tremors there this month.
“It’s been caused by the hydraulic fracking,” he said.
Critics claim fracking poses a serious risk to people and the planet through effects such as toxic air pollution, contamination of water and seismic events. It has also been blamed for lowering house prices.
Nearly 2,000 square kilometres of land across Scotland’s central belt has been earmarked as suitable for exploitation of unconventional oil and gas, though recoverable quantities have been described by the British Geological Survey as “modest” – an estimated six billion barrels of shale oil and 80 trillion cubic feet of shale gas.
It’s not known how much these reserves could be worth to the economy, but a report from financial experts at PricewaterhouseCoopers in 2013 suggested shale gas extraction north of the Border could bring in up to £5 billion by 2035.