-- Dr. Syed Saquib said he was the lone trauma surgeon on call at University Medical Center Sunday night when the hospital was notified that there was "a mass casualty situation on the Vegas strip."
It was a little after 10 p.m. and, very quickly, it became an all-hands-on-deck situation.
"We were seeing all kinds of injuries. Gun shots to the head, chest, abdomen and pelvis and extremities," Saquib told ABC News' Juju Chang during an interview for "Nightline." "[We had] walking wounded, patients that were brought in by other family, friends ... people coming through ambulance, it was a pretty surreal scene.
"This is something we deal with on a regular basis," he added. "The only difference was the higher volume."
At least 59 people were killed and 527 injured in Las Vegas Sunday night when a gunman opened fire on a music festival crowd from the 32nd floor of the Mandalay Bay Resort and Casino, in what is now the deadliest shooting in modern U.S. history.
A special education teacher, a Navy war veteran, a police records technician and a nurse who shielded his wife during the shooting are among those who were killed.
Saquib said several surgeons volunteered to come in and they quickly went to work. According to their website, UMC Hospital is the only Level-I trauma center in Nevada.
"We had multiple ORs running at one point simultaneously, taking care of patients," Saquib said. "It was a very busy night."
Concertgoers had been enjoying the final night of the Route 91 Harvest Music Festival, which was taking place across the street from the hotel, when authorities said the suspected gunman -- 64-year-old Mesquite, Nevada resident Stephen Paddock -- sent more than 22,000 country music fans scrambling for their lives.
Jason Aldean was the headliner of Sunday night's concert. Video showed him rushing off the stage amid the gunfire. Other performers from this weekend included country stars Jake Owen, Big & Rich, Luke Combs and Dylan Scott.
As ambulances rushed to the scene, first responders plugged wounds with their bare hands and used their clothing to try to stanch each other's bleeding. At least one man described a stranger who died in his arms.
In addition to gunshot wounds, victims suffered injuries from shrapnel, from climbing fences and from being trampled, said Clark County Fire Chief Greg Cassell.
An off-duty Las Vegas police officer who was attending the concert is among the dead, police said. No on-duty emergency response personnel were injured, Cassell said.
Saquib said hospitals across the Las Vegas area worked together to take in patients and assess where the most critically wounded would go for surgery.
As it turns out, Saquib said medical personnel who had been involved in treating patients after the Orlando Pulse nightclub shooting had recently given them a lecture about their experiences.
"I honestly haven’t had a chance to fully process this tragedy," he said. "I’ve been so focused on staying in the moment and on staying focused on trying to provide the best care possible for our patients. Once I’ve had a few more days to reflect on this and look back I think it’ll hit me at that point."
And Saquib was back on duty Monday night.