Energy firm Cuadrilla has resumed fracking at its site in Lancashire, it has confirmed.
Drilling began at the Preston New Road site in October but operations were halted on a number of occasions due to underground tremors.
No fracking has taken place on the site since December.
The Little Plumpton site has been the focus of repeated demonstrations, with protesters saying fracking is harmful.
What is fracking?
- Hydraulic fracturing, or fracking, is a technique to extract gas and oil from the earth
- Liquid is pumped underground at high pressure to fracture shale rock and release gas or oil within
- The Department for Business, Energy & Industrial Strategy says shale gas "has the potential to be a new domestic energy source"
- Governments in Scotland, Wales and Northern Ireland have said they will oppose fracking until further research is completed into its environmental impact
The Department for Business, Energy and Industrial Strategy (BEIS) said the UK has "world-leading regulations that ensure shale gas exploration happens in a safe and environmentally-responsible way".
However, campaign group Friends of the Earth is calling on the government to ban fracking and support renewable energy.
Spokesperson Jamie Peters said: "Fracking just isn't part of the future if we are serious about avoiding climate breakdown."
Cuadrilla said operations at Preston New Road will be complete by November, which is the date planning permission is currently set to expire, and gas flow results are expected early next year.
The firm has been calling for a review of the threshold of seismic activity at which fracking must stop.
Currently tremors measuring 0.5 magnitude or above mean fracking must be temporarily stopped while tests are carried out.
The BEIS has confirmed the Oil and Gas Authority is currently conducting a scientific assessment of recent industry data which it "will consider once completed".
Cuadrilla recently appealed for more time to be able to drill at Little Plumpton.