Mounties believe the B.C. boy whose abduction sparked an Amber Alert Thursday has already been taken over the U.S. border.

RCMP Cpl. Dan Moskaluk said 39-year-old Robert Barnett is suspected of taking his three-year-old son Alvin during a supervised visit at a hotel in the Elk Valley region at around 3:15 p.m.

The pair is then believed to have travelled south in a 2002 blue Subaru Outback.

“We believe that Barnett has taken his son and crossed over into the United States,” Moskaluk said.

“Elk Valley RCMP are currently working in conjunction with law enforcement authorities in Montana in attempts to locate [them].”

The vehicle, which has B.C. license number 347SBL, is not registered in Barnett’s name.

U.S. authorities have also issued an alert, and a message has been posted on the AmberAlert.com website stating the boy is believed to be in "imminent danger."

The suspect is described as white, 5-5 tall with green eyes, reddish-blonde haire and a scar above his right eyebrow. Police say he may be unshaven with some facial hair, and was last seen wearing a dark sweater, blue jeans and runners.

Alvin is about three feet tall and is believed to be wearing a red shirt and blue jeans.

Anyone who sees the vehicle is asked not to approach it, but to call 911 immediately.