NSW Police have uncovered more than half a dozen drug houses they allege are part of a major cannabis cultivation and distribution network operating across Sydney.

Officers from Strike Force Grassy seized more than 940 cannabis plants with an estimated street value of more than $2.5 million when they raided a series of properties across the city yesterday.

Police allegedly discovered a series of elaborate hydroponic set-ups when they raided seven homes in Guildford, Miranda, Lidcombe, Kogarah, North Strathfield, Beverly Hills and Granville.

Police allegedly discovered a series of elaborate hydroponic set-ups. ( Supplied: NSW Police )

They also arrested six people during additional raids on six other homes at Peakhurst, Padstow, Bankstown, Yagoona, Beverly Hills and Granville yesterday.

The four men and two women, aged between 21 and 26, were charged with drug offences and participating in a criminal group and were refused bail to face Bankstown Local Court today.

The arrests followed previous police operations between July and November this year in which officers seized more than 970 cannabis plants from homes in Strathfield and Merrylands.

Police say those properties are connected to the alleged syndicate which was uncovered yesterday.

Redfern Regional Enforcement Squad Commander, Detective Chief Inspector Stuart Bell, said information from the community was crucial for police to crack down on alleged drug networks.

"We are focused on the manufacturers and suppliers of illegal drugs to stem the tide of drugs at the source," he said.

"With that in mind I urge members of the public to familiarise themselves with the seven signs of a drug house.

"These include strange odours, diverted electricity, chemical containers and waste, blacked-out windows, hoses and pipes in strange places, extremely bright indoor lighting and vehicles arriving at odd hours."