GASTONIA, N.C. -- Parents leaving children in hot cars has become such a serious problem that firefighters and police in Gaston County held a demonstration to show just how dangerous it can be.

They put a thermometer on the inside of a police cruiser to gauge the temperature on the inside the car. The thermometer was visible from the outside of the car.

First they cooled down the car to 75 degrees. Then an officer turned off the car and waited.

In just four minutes, the temperature jumped nearly 20 degrees, to 92.

“The direct sunlight on the windshield and the side windows is what causes the car to heat up so fast,” said Jim Landis of the Gastonia Fire Department.

And the temperature kept rising. It didn't stop until it reached 104 degrees – in just eight minutes.

That’s hot enough, police and firefighters say, to kill a child inside.

Their message: don't take chances.

“Get your kids out of the car, even for what you think is going to be 30 seconds,” Landis said.

Even once the sun goes down it's still not safe to leave your child alone in a car. According to the Safe Kids Coalition, when it's only 80 degrees outside, it can get hot enough inside a car to cook an egg on the dashboard.

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