More than 700 cannabis plants with a street value in excess of $3 million have been seized in a police raid on a hydroponic cannabis warehouse in Sydney's northwest.

The Riverstone warehouse was raided by officers from the Middle Eastern Organised Crime Squad on Thursday morning, police said.

The warehouse was divided into seven separate rooms, each containing lighting, water filtration systems, air conditioning and chemicals associated with the indoor growth of plants.

Police found 723 cannabis plants, 643 of which were mature and they estimated the potential combined street value at approximately $3.4 million.

Investigations are continuing and arrests are expected.