O’FALLON, Mo. (AP) — St. Louis city and county officials say they will require masks in some public places starting Monday, citing a sharp increase in COVID-19 cases spurred by the delta variant.

Masks will be mandatory in indoor public places and on public transportation for everyone age 5 or older, even for those who are vaccinated, officials said in a news release on Friday. Masking outdoors “will be strongly encouraged,” especially in group settings.

The decision comes as both of Missouri’s urban areas are seeing a big uptick in cases in hospitalizations that began in rural areas of the state, especially in southwestern Missouri. The Kansas City Star reported Friday that medical leaders in that region appear to be on the verge of calling for a new mask mandate there as well.

Dr. Fredrick Echols, acting director of health for the city of St. Louis, said more than 500 St. Louisans have already died from COVID-19, “and if our region doesn’t work together to protect one another, we could see spikes that overwhelm our hospital and public health systems.”

Dr. Faisal Khan, acting director of the St. Louis County Department of Public Health, encouraged people to get vaccinated, and to adhere to the new guidelines.

“We must protect our most vulnerable residents as well as children under 12, who are not yet eligible for vaccinations,” Khan said in the release.

Dr. Steve Stites, chief medical officer at the University of Kansas Health System, said the Kansas City region is “past the tipping point,” with hospitalizations rising sharply.

In the Missouri part of the Kansas City region, information from the Missouri Department of Health and Senior Services shows that 319 people are hospitalized — nearly triple the number from early April. The number of intensive care unit patients has more than doubled since June, to 84.

“I think you are going to find the chief medical officers are going to call for a reinstitution of the mask mandates and social distancing because we had that discussion this morning and we were all in favor of it because we’re in trouble in the hospitals,” Stites said during a briefing on Thursday.

Southwestern Missouri continues to see the worst of the surge, and Republican Gov. Mike Parson announced Thursday that 10 advanced life support ambulances, 20 medical professionals, two “strike team” leaders and a logistics specialist were being sent to Springfield. Their role will be to help with transporting patients in a city where hospitals are near capacity.

They were expected to arrive Friday from Arkansas, and will remain for up to two weeks. A news release from Parson’s office said a mutual aid agreement between states “allows for the sharing of critical resources when needed.”

Springfield and Greene County earlier this month asked the state to fund an alternative care site to help handle the overflow of patients. Parson said the city and county are specifically asking that a hotel be converted into a temporary medical facility. The request has been submitted to federal emergency management officials, Parson’s news release said.

State data shows 544 people hospitalized and 222 in ICU in southwestern Missouri, numbers that exceed the worst of the winter peak of the virus.