A BC Hydro submarine cable worth $2.7 million was damaged by the thieves, said police. (Mike Laanela/CBC)

Vancouver police have arrested seven men in connection with an attempt to steal copper wire from a city power station that destroyed a $2.7-million cable.

The seven men were arrested after a Canada Line employee spotted intruders inside a BC Hydro substation on the 400 block of Kent Street around 2 a.m. PT Monday.

The employee was checking the Canada Line tracks above the substation when he saw the intruders below him loading wire into a van. He called 911 and three police dogs and several officers quickly moved in to make the arrests.

"An examination of the yard revealed that the thieves had cut through the chain-link fence and were in the process of stripping large cables to get at the copper inside. Numerous tools and hacksaws were recovered by police," said Const. Jana McGuinness.

The theft will cost B.C. Hydro, and its ratepayers, about $2.8 million, McGuinness said in a statement issued Wednesday morning.

"A damaged special submarine cable will need to be replaced at a cost of $2.7 million and a $100,000 cable has not yet been recovered," said McGuinness.

"The bigger concern is public safety," BC Hydro spokesman Dag Sharman said in the statement released by police.

"Thieves put their lives at risk, but they also put the lives of first responders at risk. Our staff who arrive at work and aren't aware that wires and equipment have been tampered with are also in danger, as is the public who may come into contact with live wires."

Sgt. John Rennie of the Vancouver Police Department's property crime unit, said metal theft is taken very seriously by the department.

"We have the Xtract program, in which all secondhand dealers, pawn shops and scrap dealers have to report all transactions. We're also involved with Scrap-watch, where scrap dealers report any suspicions to police and to each other," Rennie said in the statement.