Officers raided the former Netherton Hotel on Napier Avenue, South Shore, and found almost a thousand plants inside.

The drugs seized are believed to have a street value of hundreds of thousands of pounds.

Detectives today told The Gazette they believe the operation - which took over 12 of the hotel's 13 rooms - was into its second harvest so much of the original crop may already have found its way onto the streets.

Reclassify

The raid came on the same day the Government announced it was reclassifying cannabis from Class C to Class B, and as fears grow Blackpool is increasingly being targeted by organised crime gangs from the far east.

Seven cannabis factories have been raided locally in the last year alone, many set up in either disused business premises or rented homes.

In yesterday's raid, police found plants - growing under high-powered lights - in bedrooms, bathrooms and living quarters.

It is believed the property had been occupied by Chinese nationals over a period of months. One man is now being questioned by detectives.

Det Sgt Paddy Dowling of Blackpool CID said: "This was a major drug growing operation in what was until two years ago a successful hotel.

"The drugs will be worth thousands of pounds and this would appear to be the second harvest.

"It is one of a number of similar criminal ventures discovered in Blackpool recently and one of the biggest ever found in the resort.

"All the operations we've found so far have predominately been organised by people of Chinese or Vietnamese extraction."

The landlord of the hotel was said to have been unaware of what was going on inside his property.

Cannabis factories are being discovered at a rate of 50 a week nationally, police figures show.

Many have been set up by migrant gangs leading to fears Blackpool's to cheap rental market is an easy target.

Detectives are now warning residents to be on the look out for any suspicious activity at empty or recently rented properties.

Det Sgt Sue Cawley, of Blackpool CID, said: "We seem to have had an influx of these types of large scale growing operations in recent months.

"We think those responsible are looking for a town where they can remain pretty much anonymous like they can in Blackpool because of its transient population."

Local factories have been discovered in disused pubs, takeaway food outlets and residential homes across the Fylde coast - with police destroying crops thought to be worth more than a million pounds.

Only last week one operation - boasting 600 plants with a street value of £60,000 - was uncovered behind the curtains of a semi-detached home in Queen Victoria Road, Revoe.

Detectives are now warning residents to be on the look out for any suspicious activity at empty or recently rented properties while Blackpool South MP Gordon Marsden says he will lobby the Home Office about the legal status of marijuana seeds.

UK-based websites are currently offering buyers "Great Skunk hybrid, a must for all commercial growers" and boasting "very high yield. Big buds with a sweet taste - £24.99".

It is currently legal to buy and sell seeds in the UK, but not to germinate them. Many see this as a loophole which helps both the domestic and commercial grower.

The reclassification to Class B means the maximum prison sentence for possessing cannabis rises from two years to five years.

Since cannabis was downgraded there has been widespread concern about the increased prevalence of stronger "skunk" varieties.