The Border Patrol is begging agents to volunteer in the north after a staggering nearly-850% surge of mostly-Mexican migrants illegally crossing into the US from Canada.

The agency’s Swanton Sector in Vermont — covering parts of upstate New York and New Hampshire — requested a “quick turnaround” of agents from the already overwhelmed southern border to make their way north to volunteer for at least a month starting next week.

Help is needed to control the “strain caused by the surge” of “primarily Mexican migrants with no legal documents,” Swanton’s Chief Patrol Agent Robert Garcia wrote in a memo obtained this week by Fox News.

“Due to the increased numbers, stations are task saturated with processing large groups, which has c …