MISSION, Kan. (AP) — Just when the U.S. appears on the verge of rolling out a COVID-19 vaccine, the numbers have become gloomier than ever: Over 3,000 American deaths in a single day, more than on D-Day or 9/11. One million new cases in the span of five days. More than 106,000 people in the hospital.

The crisis across the country is pushing medical centers to the breaking point and leaving staff members and public health officials burned out and plagued by tears and nightmares.

All told, the crisis has left more than 290,000 people dead nationwide, with more than 15.5 million confirmed infections.

The U.S. recorded 3,124 deaths Wednesday, the highest one-day total yet, according to Johns Hopkins University. Up until last week, the peak was 2,603 deaths on April 15, when New York City was the epicenter of the nation's outbreak. The latest number is subject to revision up or down.

Wednesday's toll eclipsed American deaths on the opening day of the Normandy invasion during World War II: 2,500, out of some 4,400 Allied dead. And it topped the toll on Sept. 11, 2001: 2,977.

New cases per day are running at all-time highs of over 209,000 on average. And the number of people in the hospital with COVID-19 is setting records nearly every day.

A U.S. government advisory panel on Thursday endorsed widespread use of Pfizer's COVID-19 vaccine to help conquer the outbreak. Depending on how fast the FDA signs off on the panel's recommendation, shots could begin within days, inaugurating the biggest vaccination campaign in U.S. history.

In St. Louis, respiratory therapist Joe Kowalczyk said he has seen entire floors of his hospital fill up with COVID-19 patients, some of them two to a room. He said the supply of ventilators is dwindling, and the inventory is so thin that colleagues on one shift had to ventilate one patient by using a BiPAP machine, similar to the devices used to treat sleep apnea.

When he goes home to sleep during the day at the end of his grueling overnight shifts, he sometimes has nightmares.

"I would be sleeping and I would be working in a unit and things would go completely wrong and I would shock myself awake. They would be very visceral and very vivid," he said. "It would just really spook me."

In South Dakota, Dr. Clay Smith has treated hundreds of COVID-19 patients while working at Monument Health Spearfish Hospital and at Sheridan Memorial Hospital in neighboring Wyoming.

He said patients are becoming stranded in the emergency room for hours while they await beds on the main floor or transfers to larger hospitals. And those transfers are becoming more challenging, with some patients sent as far away as Denver, 400 miles (644 kilometers) from the two hospitals.

"That is a huge burden for families and EMS systems as well when you take an ambulance and send it 400 miles one way, that ambulance is out of the community for essentially a whole day," he said.

Smith added that some patients have gone from thinking "I thought this was a hoax" to "Wow, this is real and I feel terrible." But he also has seen people with COVID-19 who "continue to be disbelievers. It is hard to see that."

"At the end of the day the virus doesn't care whether you believe in it or not," he said.

New Orleans' health director, Dr. Jennifer Avegno, described a recent visit to a hospital where she watched doctors, nurses, respiratory therapists and others risk exposure to the disease in a long, futile attempt to save a dying COVID-19 patient. Some broke down in tears afterward, she said.

"These are seasoned emergency and critical care personnel," she said. "We do not cry very often — and especially not a number of us all at once."

In Illinois, where authorities recorded an additional 196 deaths Thursday, Dr. Meeta Shah at Rush University in Chicago said medical workers are already beleaguered and waiting for the "other shoe to drop" from holiday gatherings.

"Every day you think, 'Today is going to be awful,'" Shah said.

In Virginia, Gov. Ralph Northam, a doctor by training, announced a midnight curfew and expanded mask rules to require face coverings be worn outdoors, not just inside.

Pennsylvania Gov. Tom Wolf temporarily halted school sports and other extracurricular activities, ordered gyms, theaters and casinos to close and banned indoor dining at restaurants.

In Idaho, Gov. Brad Little didn't order a statewide mask mandate or enact additional restrictions despite the public health agency announcing that COVID-19 is now the leading cause of death in the state. But the Republican governor warned that if hospitals continue to fill and the state has to initiate "crisis standards of care" — when life-saving treatment would be reserved for patients most likely to survive — car crash victims could be treated in hospital conference rooms and diabetics with infections could be denied beds.

Little was among the first governors to publicly wear a mask in the spring and has encouraged others to do so, but anti-mask sentiment is intense in the conservative state.

In New York City, which was ravaged by the virus in the spring, one doctor sounded a note of relative optimism, saying that at least physicians are more capable of managing the virus now.

"Early in the spring we did not know enough," said Dr. Jolion McGreevy, who directs Mount Sinai Hospital's emergency department. "We really are operating from a place of knowledge, now — which is a big leap from where we were in the spring."

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Associated Press National Writer Jocelyn Noveck in New York contributed to this report. Associated Press journalists from around the globe contributed to this report.