The suspected shooter at the Grand Sierra Resort was among those transported to a hospital, district health officer for the Northern Nevada Public Health Department Dr Chad Kingsley said.
Officers arrived less than three minutes after the first shots rang out and fired at the suspect, police said in a statement.
Authorities did not release the conditions of the suspect or the three others who were injured.
The resort is one of Reno's most prominent venues, hosting concerts, sporting events and a campaign rally by President Donald Trump before the 2024 election.
Near the California border and just northeast of Lake Tahoe, the town is a popular summer tourist destination.
Hotel guests heard several shots coming from the resort's valet area about 7.30am.
Michael Sisco, 60, said he was in his room and about to head to the valet for his car when he heard popping sounds.
He looked out his window and saw people screaming and running from the valet area.
He said he saw a man holding his stomach and staggering before falling motionless next to a car.
Sisco moved away from the window as the gunshots continued.
"A half hour after the incident I started shaking because I realised I could've been there," he said.
"That's exactly where I was going."
Christina Martinez heard the shots just as she was stepping onto an elevator in the lobby, and they were still going off when she stepped out onto the 18th floor.
Someone in a neighbouring room told her there was a gunman right outside the main entrance, near where Martinez said she was getting coffee just moments before.
"I feel very blessed but that's kind of why I had a panic attack," she said.
"I was like, oh my God. I was just there."
Hours after the shooting, the entrance inside the casino leading to the valet area was roped off to guests and privacy screens were placed in front of the glass doors to block the view outside.
In addition to those who were killed and the people taken to the hospital, three more were treated for minor injuries at the resort, according to Devon Reese, chair of the Board of Health in northern Nevada.
One person was grazed by a bullet on their pinky finger, one was treated for severe anxiety and one was injured while running, he said.
More than a year ago, two men were charged with fatally shooting another man who was staying at the resort in January 2024.
The Grand Sierra claims to have the biggest casino floor in northern Nevada and sits just a few blocks from the Reno-Tahoe International Airport.
It is also one of the tallest buildings in the city, with nearly 2000 hotel rooms.
"My heart breaks for the victims, their families, and our entire community. Reno is strong - but we are not immune to the epidemic of gun violence gripping this nation," Reese said in a social media post.
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