Waikato police Senior Sergeant Greg Foster is holidaying in Las Vegas with family and described the "chaotic scene" to Newstalk ZB.
Foster said they're staying in the Luxor Hotel, next to where the shooter was holed up at the Mandalay.
He said they'd just gone to bed when the gunfire broke out.
"We recognised pretty early that it was gunfire but being Vegas you're never quite sure what's going on. We could hear the concert very clearly from our hotel room. Then the volley of gunfire started. It was very loud. We were very close to it. It sounded like it was directly outside our window."
Foster said they knew it was serious as the music stopped and not long afterwards concertgoers started running into their hotel as it was one of the closest venues.
Foster's first fears were for his mother, who was downstairs in the casino.
"There was a concern that the gunman was mobile by that stage so I had to go down and make sure that she was safe and got back to her room safely. There were certainly a lot of panicked people that had come from the concert. There were people that were being dragged into the hotel room; police officers were running round and telling us to go back to our room. It was quite a chaotic scene."
Foster said his experience as a policeman told him he was wearing gunfire, not fireworks.
"I'm a police officer so I know the sound of gunfire. As I say it was very loud, there was a volley of gunfire then it would stop. Then it would start. It was definitely automatic gunfire."
Foster said it seemed the shooter was either reloading or changing firearms. Either way, "it just kept coming - wave after wave after wave".
He said his family had just arrived in Las Vegas that day and had walked with some of the concertgoers and asked them where they were going.
"We weren't too sure what was going on so we spoke to a couple of them and asked them what was going on and they said they were off to the Route 91 Country Festival. [They] all seemed like a real nice crowd, all very orderly. All looked like they were going to have a good time, so yeah, it's all very sad what happened."
Speaking to the Herald from his Las Vegas hotel at 11.30am (US time), Foster said were pretty startling scenes as he walked around the scene today.
"A lot of the concertgoers are guests at the hotel. A lot of people are just walking around shocked, a lot of crying. A lot were checking out today anyway because it was the end of the festival last night so a lot of them are going home. But yeah, a few injured people walking around. It's surreal."
He said their hotel was in lockdown until 4.30am, but he popped out of his room to look into the lobby and saw rows of police officers surrounding the area.
"I went out later on and just looked into the lobby. It was quite eerie because the whole casino was completely empty and there was just a ring of police officers around the interior entrances and exits. That was pretty full on."
Foster said he and wife, Julie, a former policewoman, were amazed their boys, aged 8 and 11, slept through the whole thing.
"God knows how they slept through it all. Not only was the shooting loud but then we got put into lockdown here and that was coming through the emergency system, which is directly into our room so there was an alarm going and then were announcements through the night. They managed to sleep through it all, which was really good."
He said the reality hit when he went to find his mother in the casino. She was unaware of what was going on as she couldn't hear the shots being fired.
"The first she knew about it was when people were running through the casino panicked and she thought 'oh, that's not normal'. Then she got my phone call and just basically came back to the elevator and I met her there. Once we were in our room there was no danger to us otherwise it would have been a bit more terrifying. It's all just very sad."
When he went to bed, only two were confirmed dead.
"It wasn't until I spoke to [NewstalkZB's Larry Williams and he said there were 58. Which in hindsight, doesn't surprise us because of the number of shots and where they were directed and the concentration of people. It would have been more surprising if there were only two dead."
The Foster family were scheduled to stay in the city for four nights and saidthey would continue with their holiday as planned.
"Our family is absolutely devastated for the families who have lost loved ones in the tragedy and our thoughts are certainly with them."