With a heatwave bearing down on Chicago, Mayor Lori Lightfoot passionately warned parents Thursday morning: “Don’t leave your children in cars.”

And should you find an unresponsive kid in a closed car, don’t hesitate, she said.

“If you stumble upon something like that, by any means necessary, get the kid out of the car and call 911,” Lightfoot said at a news conference to remind residents to look after one another and take advantage city services, such as cooling centers, to escape the heat.

Temperatures were expected to climb into the mid 80s on Thursday. The real sizzle should set in Friday.

A National Weather Service excessive heat warning had been set to take effect Thursday, but was pushed back when stronger-than-expected cooling rains hit the area. Now, it is scheduled to start Friday at 10 a.m., lasting through 7 p.m. Saturday.

Daytime temperatures during that stretch are expected to rise into the 90s, with heat indexes — how hot you actually feel when factoring in humidity — reaching about 110 degrees.

The city’s heat response “an all hands on deck,” said Lightfoot, flanked by various department heads while addressing reporters at the city’s Office of Emergency Management and Communications in the West Loop.

“These are life-threatening temperatures and conditions and we all have to work together to remain safe,” she said.

City safety officials offered a laundry list of tips.

Check on neighbors, especially the most vulnerable, such as the elderly and sick. Overweight people and infants also are especially vulnerable to the heat.

Call 311 to request a well-being check, locate a cooling center, or request transport to a cooling center.

All six cooling centers operated by the city will have extended hours, staying open until 7 p.m. Thursday and Friday instead of the usual 5 p.m.

The importance of air conditioning can’t be stressed enough, said Dr. Allison Arwady of the Chicago Department of Health.

“Do not rely on a fan when the weather is this hot,” she said.

A number of public buildings such as libraries, park district field houses and police stations are also available to cool down.

“We’ve come a long way since 1995,” Lightfoot said, referring to a heat wave that killed 793 people, most of them poor and elderly residents living alone. “But we’re only as good as extending our outreach and getting the word out to community members.”

Anyone spending time outside should drink at least two to four cups of water every hour, Arwady said.

The advice was not lost on construction crews cycling through a Northwest Side coffee shop Thursday morning; all pointed to coolers filled with ice and water when asked how they planned to weather the heat.

David Gutierrez, 25, felt fortunate his roofing gig — which includes using a torch to apply the final layer — would wrap up before peak temperatures set in after lunch.

“We didn’t plan it that way. Just got lucky,” he said. “That torch adds at least another 30 degrees.”

Martin Delgado, 33, who planned to spend part of his day on rooftops installing cable television equipment, was resigned to sweating and maintain a positive attitude.

”You can’t do nothing about it, you know?” said Delgado.

Gabriel Salas, 18, gathered at a job site across the street from the Dunkin’ at Belmont and Sacramento avenues with other workers clad in jeans and steel-toe boots.

“Not the best clothes in the heat,” he said, “but safety first.”