Heroic military veterans and police officers put their training to use during the deadly mass shooting at a Las Vegas music concert — even “plugging bullet holes with their fingers,” according to a report.

“You saw a lot of ex-military just jump into gear,” witness Russell Bleck told the “Today” show on NBC. “I saw guys plugging bullet holes with their fingers.”

“While everyone else was crouching, police officers (were) standing up at targets, just trying to direct people, tell them where to go,” he added. “The amount of bravery I saw there, words can’t describe what it was like.”

The practice of plugging gunshot wounds helps to kick in the body’s defense mechanisms that prevent rapid blood loss, according to a Wired report.

Severe wounds, especially on the carotid arteries of the neck, must be quickly plugged with the fingers or packed to temporarily stop the hemorrhaging, according to Gould and Pyle’s Pocket Cyclopedia of Medicine and Surgery.

Bleck was with his fiancée Sunday night in a VIP tent at the Route 91 music festival when the couple heard what they first thought were firecrackers or a crackling amplifier, he said on the show. But when the sound didn’t stop, he realized what was going on, he added.

“That was an automatic rifle, without a doubt. He was just spraying the crowd. He was relentless. There was no stopping,” he said.

“You had five, maybe eight seconds to move from cover to cover to try to move and get out of there as he reloaded.”

More than 50 people were killed and over 400 wounded in the mass shooting, a law enforcement official said — adding that the alleged shooter, Stephen Paddock, 64, of Mesquite, Nev., shot himself in his Mandalay Bay hotel room after the rampage.