Few details were immediately available, but U.S. Customs and Border Protection spokesman Mike Milne says the crossing was closed due to police activity on the Canadian side, and the Washington Department of Transportation confirmed on its Twitter feed that traffic was being rerouted due to the shooting of a border agent.
The Royal Canadian Mounted Police were planning a news conference to discuss the shooting. Initial news reports indicated that the female agent was wounded, and that the suspect then fatally shot himself.
"I am deeply concerned by the news of the shooting today at the Peach Arch border crossing of a (Canadian Border Services Agency) officer," Canadian Public Safety Minister Vic Toews said.
Washington state Department of Transportation spokeswoman Kris Olsen said it will be up to Canadian border officials to determine when the crossing will reopen.
"We're telling people they obviously need to use other routes to get across the border," she said, adding that the State Route 543 and State Route 9 entrances were open.
The Peace Arch crossing in Blaine, Wash., is third busiest port of entry on the northern border. The U.S. and Canada are connected by a park featuring an arch that straddles the international line.