Police say the driver of the single tractor trailer unit was taking the dangerous load to a local mine at about 6 p.m. PT Thursday when the truck veered off Highway 97 near Westcoast Road in Wildwood, B.C.
The driver was pinned in the truck and was extracted and airlifted to Vancouver General Hospital with serious injuries.
Police shut down traffic in both directions on Highway 97, 14 km north of Williams Lake, and established a local detour.
A nearby elementary school was also closed Friday.
Ammonium nitrate is hazardous to inhale or touch and can be extremely explosive when in contact with heat or an ignition source.
RCMP Insp. Warren Brown says the risky part of the cleanup involves hazmat crews attempting to transfer the chemicals to another truck.
"My understanding is, once an empty truck arrives at the scene to transfer the content of hazardous material from the damaged vehicle, that may require an evacuation order because the substance is very volatile," he said.
"The vulnerable area is about a 400-metre area."
Brown said police worked with the regional district and determined that evacuation orders needed to be issued to those on properties within the danger zone.
He estimates that between a dozen and 50 homes are affected, and that the evacuation orders will remain in effect for six to eight hours.
"It's probably the most volatile part of the process right now. So, the substance that's being transported, it's when it becomes most vulnerable. So that's why the precaution of evacuating the residents in the area is being taken," Brown said.
Members of the Central Cariboo Search and Rescue are assisting the police in carrying out the evacuation order.
Police are asking the public to cooperate with the evacuation order, and are reminding the public that it is illegal for children under the age of 18 to remain in an evacuated area.
Officials with the Cariboo Regional District said people requiring shelter or food can go to the Salvation Army at 267 Borland Street in Williams Lake.