Three men from Surrey, B.C. were charged Thursday in Washington state with conspiracy to distribute and import marijuana.

The charges come after American authorities on Wednesday shut down an underground tunnel crossing the U.S.-Canada border which was used in a drug-running operation.

"This is the first tunnel ever discovered between Canada and the U.S.," said a U.S. Justice Department release.

The sophisticated 110-metre tunnel runs from a depth of one to three metres and is reinforced with iron rebar and 2x6 wood supports.

The U.S. Justice Department said 42 kilograms of pot were transported through the tunnel and then loaded into a van. 

The van drove to the Bellis Fair Maill in Bellingham, Wash., where the marijuana was loaded into another vehicle. That second vehicle was stopped by the Washington State Patrol and the pot was seized.

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 was also involved in the investigation.

In a news conference, U.S. authorities revealed that the tunnel begins under a Quonset hut in Langley, B.C, and ends beneath the living room of a house in Lynden, Wash.

The building on the Canadian side is located near 264th Street and Zero Avenue in Langley, south and east of Vancouver.

Authorities had been watching construction on the site for eight months.

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

Neighbours said they had suspicions about the property for some time, but were surprised when they heard what's alleged to have been going on inside. They described the man who resided in the building as being about 30 years old.

"I never thought he had a tunnel, never," an area resident told CTV Vancouver. "That just stuns me."

Another neighbour said the building was suspicious "for a long time," adding that the news of the investigation "doesn't surprise me a bit."

Francis Devandra Raj, 30, Timothy Woo, 34, Jonathan Valenzuela, 27, were scheduled to appear in court in Seattle on Thursday afternoon.