This underground grow-op in B.C.'s southern Interior contained about 3,000 plants, police say.This underground grow-op in B.C.'s southern Interior contained about 3,000 plants, police say. (RCMP)

A massive marijuana grow operation has been found in a vault hidden beneath a workshop in B.C.'s southern Interior, police say.

The grow-op, near Sicamous, contained more than 3,000 plants and was accessed through a hydraulically operated steel door in the floor of the workshop, RCMP Cpl. Chris Newell said Wednesday.

The grow-op, which police raided Tuesday, was about 7,000 square feet in size, Newell said.

He said it was a sophisticated operation, containing fans, lights, air-conditioning units and an underground venting system.

An RCMP officer exits the marijuana vault through a hydraulically operated steel door.An RCMP officer exits the marijuana vault through a hydraulically operated steel door. (RCMP)

Four people were arrested at the scene and a fifth person turned herself in to police later Tuesday.

Those arrested face charges relating to marijuana possession, cultivation and trafficking, said Newell. They have been released and are scheduled to appear in court Aug. 17.

Sicamous is about 275 kilometres northeast of Vancouver.