(AP) — A dramatic surge in coronavirus cases has sidelined more than 800 Los Angeles city police and fire personnel and led to slightly longer ambulance and fire response times, adding to concerns about shortages of critical staff including health care workers.

Mayor Eric Garcetti said Thursday that more than 500 LAPD officers and other police employees and nearly 300 firefighters were off-duty after testing positive for COVID-19, though he said measures were being taken to ensure the safety of the public.

“This is an incredibly tough moment,” Garcetti said. “The omicron variant has taken off like wildfire.”

The surge of cases in the country’s most populous state is threatening to overwhelm hospitals. State officials on Wednesday extended an indoor mask mandate into mid-February as the omicron variant also sidelines health care workers, leading to hospital staffing shortages that could become a bigger problem.

“We are and continue to be concerned about our hospitals,” Health and Human Services Secretary Dr. Mark Ghaly said. “Some facilities are going to be strapped.”

Public Health officials across the state have advised residents to avoid visiting emergency rooms for COVID-19 tests or treatment that could be handled by a family doctor, telemedicine or at urgent care clinics.

California’s confirmed cases have shot up nearly 500% in the last two weeks and hospitalizations have doubled since Christmas to more than 8,000.

State models forecast hospitalizations could top 20,000 by early next month, a level nearly as high as last January, when California experienced its deadliest surge.

California had the lowest per-capita case rate in the U.S. in September, but like the rest of the country it’s now experiencing a dramatic rise from the new variant. It now ranks 29th in new cases per capita over the past two weeks.

Los Angeles city firefighters were working voluntary overtime shifts and others were being forced to stay on duty after their shifts ended to maintain staffing, Chief Ralph Terrazas said. He also planned to cancel approved vacations.

The absences were forcing some fire engines and ambulances to be out of service for 24 hours but all firehouses remained open, Terrazas said.

Ambulance response times have slowed 13 seconds from a year ago and fire calls are six seconds slower.

Police Chief Michel Moore said it was taking an average of three weeks for officers struck with COVID-19 to return to work, but they have not yet forced others to stay on the job to meet the demand.

“That lever is still before us,” he said. “I will not suggest to you that we would want to endure the current shortages of personnel for months on end. … We do see this as a surge that will be, it is our hope and belief, short lived.”

The Los Angeles County Fire Department, which is separate from the city department, has 450 firefighters absent after testing positive, acting Assistant Chief Brian Bennett told the Carson City Council on Tuesday, according the Los Angeles Daily News.

In Fresno County, more than 300 workers at area hospitals were out recovering from COVID-19 or isolating because of exposure to the virus, said Dan Lynch, the county’s emergency medical services director.

Ambulance personnel will likely be asked to assess patients and only transport people with true emergencies to ER departments.

The Grammy Awards, scheduled for Jan. 31 in Los Angeles, were postponed indefinitely Wednesday because of health and safety concerns and the NFL said it was looking into alternative sites for next month’s Super Bowl scheduled in LA.

While the league finds back-up venues every year, it could come into play if there are attendance restrictions, though Garcetti said he doubted it would be moved.

“I’m confident that will happen here and that we’ll be able to have a great Super Bowl celebration,” he said.

Ghaly encouraged unvaccinated people to get inoculated and others to get booster shots if they haven’t already received one to either prevent or lessen the impact of an infection. He said the vaccines and therapeutics to treat COVID-19 are all part of an approach largely absent a year ago and there is no discussion of further restrictions.

Los Angeles said it would begin requiring employers to equip workers in close quarters indoors with medical grade masks by Jan. 17.