People are advised to avoid prolonged exposure outdoors, stay in air-conditioned rooms, drink plenty of fluids and to check up on relatives, friends, neighbors and pets.
Weather officials offered the advise as expectations of heat-related illness increase.
Most of the state is affected by heat-related advisories effective until early in the week.
An excessive heat warning means dangerously hot temperatures are expected for a prolonged period of time, according to the weather service. Heat indices in some areas are expected to peak between 105 and 112 degrees while the warning is in effect, and overnight lows are not expected to fall below 75.
Mosst of the state, save the counties bordering the Texas panhandle and Jackson and Greer counties, is under a heat advisory effective until Monday, according to the weather service.
A heat advisory is similar to an excessive heat warning, but the temperatures are not as extreme. Still, heat indices are expected to peak between 105 and 109 degrees across the advisory area, according to the weather service.
Heat illnesses, ozone alert in Tulsa
The Emergency Medical Services Authority treated at least six people Friday in Tulsa for heat-related illnesses, including an infant and an 87-year-old patient, according to a news release. The illnesses, combined with the worsening forecast, prompted the authority to issue a heat alert.
Also, the Oklahoma Department of Environmental Quality has issued an ozone alert today in the city.
An ozone alert means weather conditions are favorable for ozone levels to build up close to the ground, which can be a hazard to people with respiratory problems and vegetation.
The weather service advises to curtail unnecessary driving or to carpool, refuel vehicles in the evening and avoid operating gas-powered lawn mowers and other small motors.