Authorities in the United States have busted a drug-running operation on the border of Washington state and British Columbia that allegedly used an underground tunnel to transport marijuana.

CTV News Vancouver confirmed that RCMP officers were involved in the Wednesday bust, which was led by the U.S. Drug Enforcement Agency (DEA). Homeland Security is also involved in the investigation.

A greenhouse targeted in the search is located near 264th Street and Zero Avenue in Langley, B.C., south and east of Vancouver. The town on the U.S. side of the border is Lynden, Wash.

The tunnel was described as sophisticated and well-maintained. Authorities had been watching construction on the site for eight months.

Authorities haven't yet revealed the dimensions of the tunnel, but a source told the Associated Press that it ran from the building on the Canadian side, and ran south to a house on the U.S. side about 90 metres from the border.

The Seattle Times reported the tunnel was almost a metre wide and 1.5 metres high. It had a concrete floor, wood-beam supports, ventilation and video security systems.

The Times also reports that investigators used a machine that can "see" underground, a video-equipped robot, a drug-sniffing dog and an air horn to find it.

AP reported that authorities had been monitoring construction of the tunnel for eight months. The tunnel was shut down Wednesday shortly after it opened, a government source told AP, adding that three to five arrests were made.

The DEA is not providing any further details, but the U.S. Attorney handling the case will speak at a news conference in Seattle this morning.

The DEA and the White House have complained previously about the volume of Canadian marijuana (known as "B.C. Bud") entering the U.S. through Washington state.

An estimated 880 to 2,200 tons of marijuana are grown in Canada annually, according to a report in Time magazine last year. Police estimate 90 per cent of the crop ends up in the U.S.

White House drug czar John Walters once blamed the high potency of "B.C. Bud" in part for a rise in marijuana-related emergency room incidents. "Canada is exporting to us the crack of marijuana," Walters said.