Fracking at a gas exploration site in Lancashire has been halted again after another tremor was detected underground.
Energy firm Cuadrilla resumed hydraulic fracturing at Little Plumpton on Monday after it was paused when an earthquake, recorded as 0.8 magnitude by the British Geological Survey (BGS), was detected on Friday.
But a spokesman for the firm said work had stopped again as a micro-seismic event measuring 1.1 magnitude was detected at about 11.30am on Monday.
The tremor is the largest recorded at the site since fracking began on October 15.
The spokesman said: "This is the latest micro-seismic event to be detected by the organisation’s highly sophisticated monitoring systems and verified by the British Geological Survey (BGS).
"This will be classed as a 'red' event as part of the traffic light system operated by the Oil and Gas Authority, but as we have said many times, this level is way below anything that can be felt at surface and a very long way from anything that would cause damage or harm.
"In line with regulations, hydraulic fracturing has paused for 18 hours now, during which seismicity will continue to be closely monitored by ourselves and the relevant regulators.
"Well integrity has been checked and verified."
Anti-fracking campaigners argue the process, to extract shale gas, poses risks to the environment.
According to the BGS, earthquakes with magnitude of less than two are not usually felt and, if they are, it is only by people very close to the earthquake.