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.
Caudrilla 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.