A US police force has jokingly urged criminals to “hold off until Monday” as the east coast is gripped by a deadly heatwave, which has already claimed the lives of at least six people.

A message posted on Braintree Police Department’s Facebook page read: “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,” the department’s Facebook post read. “Stay home, blast the AC, binge Stranger Things season 3, play with the face app, practice karate in your basement We will all meet again on Monday when it's cooler. Sincerely, The PoPo.”

Authorities across the country are urging residents to stay cool and hydrated after the excessive heat caused four deaths in Maryland, one death in Arkansas and another death in Arizona, CBS News reported on Saturday night.

Summer festivals and outdoor events were cancelled on Sunday, including the New York City triathlon and the OZY fest, featuring musician John Legend and US women’s soccer star Megan Rapinoe. The 1969 moon landing commemoration in Times Square was also cancelled on Saturday.

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

Meanwhile in Boston, public pools were opened to the public at no cost as temperatures were set to reach 100 degrees Fahrenheit (38 degrees Celsius), the Associated Press reported.

A US flag flies overhead as people enjoy the Astoria Pool on a hot afternoon in the New York City borough of Queens (AFP/Getty Images)

The National Weather Service described the heat wave as “oppressive and dangerous” and warned states from the Carolinas to Maine would feel temperatures of 100 to 110 degrees Fahrenheit (38 to 43 degrees Celsius).

Chicago also saw many outdoor event cancellations, including a run in Grant Park. While the city saw a record 700 deaths during a three-day heatwave in 1995, none were reported from the region as of Sunday.

Baltimore reached a heat index of 122 degrees Fahrenheit (50 degrees Celsius) by early Saturday afternoon. CBS News reported record heat in “New York City's JFK Airport, Long Island's MacArthur Airport, Atlantic City, Blacksburg, Virginia and Millinocket in northern Maine.”

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A cold front brought some relief to the central US, the National Weather Service reported, as temperatures cooled off in the Upper Midwest and Great Lakes.