The shooter who targeted a crowd of concertgoers from his Las Vegas hotel room on Sunday night rained fire down for 15 to 20 minutes, Randy Sutton, a former Las Vegas police officer, told CBS News. That made it difficult for paramedics to approach victims, he said. “Many of these injured were taken by civilians,” Sutton said. “There simply weren’t enough ambulances to get there in time.”

Among the more than 500 people who were injured, more than 100 victims were transported about seven miles north to University Medical Center. At least 30 went directly to Nevada’s only Level I trauma center. (A Level I trauma center is designed to treat the most severe injuries, including stabbings and bullet wounds. It is staffed round-the-clock by general surgeons and has many specialists on hand).

Some of the victims sustained injuries from being pushed and trampled, but most of the injuries were caused by bullets, according to a hospital spokeswoman. “We’ve been very busy all night long,” the spokeswoman told NBC’s “Today” program, adding that UMC’s trauma unit has three operating rooms, along with an “adequately stocked” blood bank and MRI and CT equipment.

UMC served 12,500 patients last year, according to its website. The trauma center treated 2,082 patients in 2015, the Las Vegas Sun reported last year. UMC has seen a declining volume of trauma patients since two other hospitals, Sunrise Hospital and St. Rose-Siena, opened lower-level trauma centers more than a decade ago. Trauma care experts have questioned whether Las Vegas is adequately equipped, arguing that “adding trauma centers would increase the community’s resilience in the event of a disaster.”

Another 180 victims were treated at Sunrise Hospital and Medical Center, a Level II Trauma Center located a few miles from the Strip. Trauma doctors, nurses, and other hospital staff scrambled all night, performing about 30 surgeries, the hospital’s CEO said in a press release. Fourteen of the patients have died.

Sunrise’s owner is reportedly requesting a special waiver to allow out-of-state doctors to fly in to assist with the onslaught of patients.

Many of the victims suffered gunshot wounds, which can be physically and economically devastating. For the estimated 80,000 Americans who are shot each year and survive, the cost of one initial hospitalization can run anywhere between $16,800 and $33,462. Some of the most expensive injuries are caused by assault firearms, which cost $32,000 per hospital admission on average.

The cost of gunshot wounds extends much further. Many gunshot victims also need intense physical therapy, counseling, and caretakers.

As medical professionals throughout Las Vegas continue to treat physical wounds, locals are mobilizing to address the invisible trauma provoked by the shooting. The Mandalay Bay Resort and Casino, the hotel where the massacre took place, posted a call on Twitter for certified trauma counselors. The resort set up two crisis phone lines, as well.