The South Western Ambulance Service says some emergency vehicles have been obstructed by drivers queueing for takeaways and drive-thrus.
The emergency service is urging people to think twice about the way theyare positioned on the roads.
It says "What costs you a fiver could cost a patient their life."
McDonald's, KFC, Costa and Burger King have reopened many stores across the country.
The KFC Drive Thru Crownhill branch on Tavistock Road in Plymouth saw huge queues to the Crownhill Retail Park on Tavistock Road - a main route to Derriford Hospital which stretched more than two miles.
An ambulance service statement asked drivers to consider the following when parking:
Junctions - is there clear access so an emergency vehicle can cross unobstructed or pull in or out?
Traffic lights - leave enough space behind the stop line so emergency vehicles can get through if needed, but never go through a red light for an emergency vehicle.
Leave enough space in front of you for an emergency vehicle to pull in when overtaking if traffic the opposite side of the way doesn’t stop.
In two lanes of the same flow, stay alert in case services are trying to get through. Keep music down and have the window open a bit if practical.
This is not the first time the SWAS has appealed for drivers to be more mindful when parking.
The service says that when it comes to takeaways or drive-thrus "if it's too busy and it's unsafe to queue because of traffic, please go back later".
It could be your family we are trying to get to or are critically ill in the back of an ambulance.