Sophisticated drug factories are harvesting cannabis plants worth millions of pounds across West Yorkshire.
Organised gangs are using derelict buildings and houses to produce the class B drug on an industrial scale.
And police said the cultivation is being carried out by modern day slaves who have often been trafficked into the country and work the farms to pay off their debts for entry into the country,
Figures showed between January 1 and June 21, 2014, officers raided 387 cannabis farms in the region.
This included 61 busts in Wakefield, 46 in Calderdale and 15 in North Kirklees.
During the same period in 2015, police also uncovered 387 farms including 54 in Wakefield, 39 in Calderdale and 25 in North Kirklees.
Police are now warning people to be on the look out for the production of drugs in their communities.
West Yorkshire Police force drugs co-ordinator Bryan Dent said: “Cannabis is harmful to individuals, harmful to our communities and has intrinsic links to organised crime groups.
“The tactics and expertise we have developed over the years have seen us have significant successes in identifying and shutting down cannabis farms, and that work will continue.
“Those involved in the production of cannabis are more likely than ever to get caught and will face significant penalties through the courts.”
During the past three months three £1m cannabis farms were shut down by police in Wakefield alone.
Police raided a multi-million pound factory at two derelict buildings behind the two old ABC Cinema, Kirkgate, in April this year.
It was followed by the discovery of drugs farms at Millennia Park Industrial Estate in Thornes and another at an industrial unit in Horbury, in June.
All three buildings contained thousands of plants with the potential to produce cannabis worth millions of pounds.
In Calderdale, businessman Stephen Hill was jailed for two years last month after being caught smuggling cannabis to the Isle of Man.
Police raided his home in Market Street, Hebden Bridge, and found 4.5kg of skunk cannabis and £7,000 in cash. Hill had also been growing eight cannabis plants at the house.
And three men were jailed for producing cannabis in Cleckheaton and Dewsbury in an operation worth more than £100,000 last year.
Police uncovered a cannabis farm at a unit in Headfield Mills, Cleckheaton, where plants worth an estimated £60,000 were seized in 2012.
They also found equipment that was used to grow another farm on Tofts Road, Cleckheaton, which produced plants worth £31,000.
Riki Williams, of Cornmill Drive, Liversedge, was jailed for four years and eight months; Simon Hepworth, of Sykes Street, Cleckheaton, was jailed for three years and two months and Joseph Cox, of Occupation Lane, Chickenley, was jailed for six years and three months.
Mr Dent said receiving information from the public was vital in helping shut down drug operations.
He said: “A key part of our work to tackle the issue is the information we receive from communities about residential or commercial premises that appear to be being used for the production of cannabis. We encourage people to keep letting us know their suspicions so we can act.”
Anyone with any information should call police on 101 or Crimestoppers, anonymously on 0800 55111.
How to spot if you have a cannabis farm next door
Blacked out windows and a distinctive sweet smell are some of the tell tale signs of cannabis farms.
Hundreds of drug dens are set up across West Yorkshire each year, some harvesting plants worth millions of pounds.
Police are urging people and landlords to look out for the signs of drug operations near their homes.
West Yorkshire Police force drugs co-ordinator Bryan Dent said: “Cannabis is an unsafe drug, particularly for our young people to consume and cannabis farms attract other serious crime to our communities in addition to being a fire risk.”
High levels of heat and condensation, a constant buzz of ventilation and lighting equipment being taken into homes are other signs of cannabis farms.
Landlords need to check the identification of potential tenants and Mr Dent said they should be cautious of people asking to pay with cash up front for long term rent.
He said: “If a cannabis site is established in your premises, you will find that lots of damage will be caused and there is the definite possibility of a fire resulting. The landlords often find themselves suffering significant loss after their premises have housed a cannabis farm, due to both damage and their inability to re-let. I always remind people that if they have any suspicions to report it to the police. You could be alerting the authorities to offences of human trafficking and modern day slavery, which often starts at the other side of the world. We regularly find individuals inside cannabis farms who have been smuggled into the country and are working of their debt before they are freed from the premises by the crime group.”