(CBS Local) — As much of the country swelters in hot and humid temperatures this summer, firefighters are warning people to not leave plastic water bottles in cars during extreme heat.

First responders say leaving a plastic bottle of water in a hot car in direct sunlight can start a fire in just a couple of minutes.

In order for that to happen, firefighters say the bottle would have to be full. The water and plastic could then create a magnifying effect, which could essentially set catch upholstery or plastic inside of the vehicle on fire.

“The ignition temperatures of those items are about 400 degrees so it would take some time to achieve that and you need low humidity, dry heat, but it is possible that it would start a fire,” Jay Symonds, a firefighter in Manlius, New York, told WSTM.

The Midwest City Fire Department in Oklahoma conducted a test in August 2017 and shared the results on Facebook.

“Vinyl generally starts to burn at 455 degrees,” David Richardson of the Midwest City Fire Department told CBS News. “It wouldn’t take very long to start a fire if conditions were right — depends on how focused that beam of light is.”

Richardson burned a hole through a piece of paper using a small plastic bottle.

“The air temperature doesn’t matter,” Richardson explained. “It works just like a magnifying glass, like one that you would use to burn leaves as a kid. It’s the same principle.”

Experts suggest putting bottled water in the trunk instead if it has to be kept in the vehicle.