The National Weather Service has baked biscuits inside a hot car, in a safety message about the peril of leaving children or pets inside a vehicle.

As a heatwave takes grip of large swathe of the US, with up to 200m people expected to be affected by a heat index of up to 115f degrees (46c), the officials performed the experiment inside a car in Nebraska to show how hot vehicles can become when left unattended.

To demonstrate the dangers, the NWS staff set about baking the biscuits in the city of Omaha, using only heat from the sun.

“If you are wondering if it’s going to be hot today, we are attempting to bake biscuits using only the sun and a car in our parking lot,” NWS Omaha said on Twitter. “We will keep you posted with the progress.”

CNN said four biscuits were placed on a baking sheet on the dashboard of a car and left to sit in the sun. After 60 minutes, the pan had reached 175.2f (80c) and the tops of the biscuits reached 153f. The back seat registered 120.4f in the shade.

Photographers stories of capturing extreme weather Show all 8 1 /8 Photographers stories of capturing extreme weather Photographers stories of capturing extreme weather "I stumbled on the firefighter in front of the burning home on the second day of the Camp Fire in a town called Magalia which is about five miles from Paradise, California. There were about five or six homes burning and firefighters were trying to save the houses near to those that were on fire. The heat from the fire was so intense that the firefighter could only stand near the burning building for 10-15 seconds before having to move away" - Justin Sullivan Getty Photographers stories of capturing extreme weather "This was only one of several large-scale forest fires in Brandenburg state in Germany last year, following droughts which left the forests in the region extremely dry. The year set a new record for fires that burned over 400 hectares. As a photojournalist covering the region for over 15 years, I now have to assume either drought or floods will very likely be a part of the news we will be covering every summer" - Sean Gallup Getty Photographers stories of capturing extreme weather "This photograph was taken at a sunflower field at Goersdorf near Golssen in Germany. The farmers in the region are really despairing. In the years before many faced floods, in 2018 it was scorching heat. Many grow crops that are meant to feed their cows, so when the crops fail they need to buy feed. With the price of milk so low many are fearing for their economic survival if weather cycles like this continue" - Sean Gallup Getty Photographers stories of capturing extreme weather "On the third day of the Camp Fire the flames had moved away from the town and were burning in the nearby hills. I captured this photo in Big Bend, as the story was shifting away from the fire itself and focusing on trying to locate missing persons and recover remains of those who had perished" - Justin Sullivan Getty Photographers stories of capturing extreme weather "You can see the Belchatow power plant and the rising steam and smoke from over 20km away. I went there the day before the start of the United Nations’ climate conference in Katowice, which took place in a region where coal has a long history and coal mining is woven into local tradition. Poland has made some strides with renewables, such as with wind turbines that now dot portions of the western Polish countryside. However, given how heavily Poland still relies on coal, it is unlikely that Belchatow will close anytime soon. According to a recent study by the European Commission Belchatow is Europe’s biggest single emitter of CO2" - Sean Gallup Getty Photographers stories of capturing extreme weather "I stayed the night at an alpine hut near the Waxeggkees glacier in Austria. An employee I talked to at night said, sometimes (this was August) she heard the sounds of ice breaking off the glacier and crashing across rocks. 100 years ago the glacier would have filled the photo. Now it takes over an hour to walk up to where the glacier begins" - Sean Gallup, photographer Getty Images Photographers stories of capturing extreme weather "I came across Mr. Helmut Kujat, 78, by chance after I photographed a parched farm nearby. He’s actually pouring the water into a tube that helps to better let the water reach the roots of the tree. He waters the trees in front of his house almost daily throughout spring and summer due to droughts and heat waves" - Sean Gallup Getty Photographers stories of capturing extreme weather "I took this photo about a week after the Camp Fire tore through the town of Paradise, California in November last year. It was the first opportunity to use a DJI Mavic Pro 2 drone to view the widespread devastation since the air space around the burn zone had been closed" - Justin Sullivan Getty

It said, four hours later, the tops of the biscuits were nearly finished baking, but the bottoms remained doughy.

The car had to be turned around to adjust for the changing angle of the sun.

The experiment was carried out to warn people about the dangers of leaving children or pets inside vehicles, even for for a short period of time. US summers frequently come with stories of tragic deaths as a result of a toddler or baby being left in a car.

CBS News said six people had died in connection with the heat – four people in Maryland, one in Arizona, and another in Arkansas.

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Several events were cancelled in New York City, including OZY Fest and the NYC Triathlon.

The NWS said the east coast and midwest are likely to see temperatures in the upper 90s, combined with high humidity. Experts are urging people to limit their time outside and drink lots of water.

Cities in Vermont and New Hampshire are opening shelters where people can cool off. Some power outages have been reported in Philadelphia and after storms in Michigan’s Lower Peninsula.

Police in Braintree, Massachusetts, asked residents “to hold off” all criminal activity until the extreme heat is over.

“Folks. Due to the extreme heat, we are asking anyone thinking of doing criminal activity to hold off until Monday,” the department wrote on Facebook. “It is straight up hot as soccer balls out there. Conducting criminal activity, in this extreme heat is next level henchmen status, and also very dangerous.”