Lake Illawarra police conducted a search warrant at a unit block on Waverley Drive where they found a "sophisticated" hydroponic set-up.

A 41-year-old man, who is believed to live at the units, let police into the complex about 9am.

Acting Inspector Paul Brodie said police found and seized 47 cannabis plants of various sizes, five kilograms of dried cannabis leaf and an imitation firearm, drug paraphernalia and hydroponic equipment in the four units.

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The man, who is renting the units, was arrested accused of growing and possessing a prohibited drug.

"Anyone who goes to such efforts as to establish a hydroponic set-up is sophisticated and there is a lot of time and effort that goes into maintaining the set-up," Acting Insp Brodie said.

"Over 50 cannabis plants is considered commercial quantity so this being just below that is fairly serious.

"This was a good bust and anytime a firearm is taken into police possession is a win, even if that firearm is an imitation."

Some of the plants were growing in pots set on top of milk crates while others were on the ground.

Some plants were growing under lights.

Acting Insp Brodie said it was a good the drugs had been seized by police rather than ending up in the community.

"This was a pretty sophisticated set-up," he said.

"[Whoever did this] has gone to a lot of effort to get the infrastructure, build it up and maintain the hydroponic plants.

"It would have cost a fair bit of money."

Acting Insp Brodie said police believe only the man they arrested was involved in the operation and are not looking for any other suspects.

Police were at the units collecting evidence until 1pm.

The man was taken to Lake Illawarra Police Station where he has been charged with cultivating prohibited plant, supplying cannabis, two counts of possessing prohibited drug and possessing unauthorised pistol.

He was refused bail to appear before Wollongong Local Court on Friday.