U.S. Border Patrol spokesman Eric Dorais said that at around 9:10 a.m. PT, U.S. border agents encountered two men wearing camouflage clothing and backpacks in the Columbia Valley area, approximately 12 kilometres east of the Huntingdon/Sumas border crossing.
"One of the subjects fired at the agents and fled into the woods," Dorais said in a written statement.
The other individual was taken into custody, he said. No injuries were reported.
Abbotsford police Const. Ian MacDonald says his department was then notified that the second suspect may have fled toward Canada.
Abbotsford police and the RCMP responded by setting up roadblocks in the area, and Upper Sumas Elementary School was locked down.
A statement posted on the school's web site said: "A police officer is stationed at the school currently as a precaution; parents/guardians are asked to respect the lockdown conditions and not attempt to access the school at this time."
Several helicopters are involved in the search, including a U.S. Blackhawk helicopter on the American side of the border.