Ambulance response times in north and east Lambton may be delayed due to poor road conditions.
The County of Lambton said calls would be prioritized on Thursday, and crews are monitoring road conditions and working closely with public works to ensure safe passage.
The county is asking residents to only call 911 in an emergency.
Emergencies include a potential threat to life or limb -- chest pain, unconsciousness, shortness of breath, severe bleeding.
Non-emergency calls may include complaints like minor injuries or general illness.
Non-life-threatening medical concerns can be directed to 811 for Telehealth Ontario who can provide an assessment and treatment options over the phone.
