Denver Police Department investigators place evidence markers while working the scene of a mass shooting early Tuesday in Denver. David Zalubowski/Assocated Press

DENVER — At least 10 people – including a suspect – were wounded in a shooting early Tuesday that police believe may be connected to a fentanyl drug deal that was taking place amid thousands of revelers amassed in downtown Denver, turning jubilant street celebrations of the Nuggets’ NBA championship victory potentially deadly.

Three victims initially were hospitalized in critical condition, Denver police said, after at least 20 shots were fired near the intersection of Market and 20th streets. All the victims were expected to survive following a rapid emergency medical response that led to four concurrent surgeries, city officials said at a briefing Tuesday.

Five people remained hospitalized midday Tuesday in fair condition, Denver Health Medical Center chief surgeon Eric Campion said. “Every patient that went to the operating room had serious and life-threatening injuries,” Campion said.

Police took two men into custody and recovered fentanyl pills, some of them packaged in bags, and several handguns. One of the suspects was wounded.

Ricardo Vasquez, 22, was stopped while running from the scene by police at Park Avenue and was arrested for possession of controlled substances and weapons as a previous offender, and Raoul Jones, 33, was being held for possession of weapons by a previous offender, police said.

“At least 20 shots were fired. We are still working to determine the motive. There appears to be a drug nexus,” Denver police major crimes division commander Matt Cark said.

Thousands of people had gathered about a mile north of Ball Arena, where the Denver Nuggets beat the Miami Heat on Monday night to win the NBA championship. Some of the revelers swung from stoplights shortly before midnight.

Fights broke out and multiple shots were fired after the altercation involving several people near 20th and Market around 12:30 a.m., police spokesman Douglas Schepman said.

Thousands still were in the area around Market and 20th celebrating, though crowd numbers had begun to decrease when that fight broke out.

“I thought it was safe when I went out last night. We had all that armory that was out there, all the police officers, basically like a military guard,” downtown resident Scott Dangelo, 55, said in an interview Tuesday morning.

He was walking near concrete barriers beside police officers shortly after midnight, without his hearing aids in.

“I thought it was just more fireworks going off. The percussion kind of startled me. … The police officers were dropping down on their knees. I’m live-streaming. Next thing I know the officers dive in and are pointing their weapons. They were pointing to where the shots were. A lady got shot, like, 10 feet away from me. Another person was struck. It was pretty crazy,” Dangelo said.

“I had an asthma attack because of all the gunpowder,” said Dangelo, who sometimes uses a respirator and who has lived downtown for years and experienced riots following the first Colorado Avalanche Stanley Cup victory and Denver Broncos Super Bowl victories.

“This was pretty, I don’t know how to put it into words. … The police officers were, like, diving down in front of me reaching for their weapons. I was trying to figure out what was going on. I thought they were pointing weapons at me. I thought they thought maybe I had a gun,” Dangelo said.

He estimated more than a dozen shots were fired. He saw bullet casings near where he crouched, shooting video and photos that police later asked him to share as evidence to help with their investigation.

“It was sad. … Something needs to be done,” he said. “I did not expect a major shooting with so many victims.”

The morning after the shooting, stains that appeared to be blood still were spread across the sidewalk along Market Street between 20th and 21st streets. Spilled food, broken glass bottles and abandoned scooters littered the sidewalks in the area.

A power washer could be seen cleaning off a patio table in front of ViewHouse, directly across the street from the largest blood spatter, and crews from the Denver Department of Transportation and Infrastructure were repairing the street poles at the intersection of 20th and Market, replacing signs and lights after people climbed on them during the celebrations.

Down the street near Market and 19th Street, more stains that appeared to be blood covered the sidewalk.

Before the shooting, Denver police, anticipating possible post-game trouble, “had staffed up significantly,” Schepman said. “We had a lot of officers in that immediate area of 20th and Market when the shooting occurred, which is why the response to it was so quick. …. We had a plan to manage the flow of traffic from the Ball Arena out to the highway and down Speer Boulevard.”

In the crowd near 20th and Market, he said, “People would start, like, a small fight. And officers would go in and extinguish and disperse that.”

Police Chief Ron Thomas said careful planning made a difference. “What we couldn’t have planned for was a drug deal right in the middle of the celebration.”

Other incidents reported nearby downtown overnight included smashing out vehicle windows and a separate shooting on Tremont Street, which left a man hospitalized. Police were investigating the circumstances that led up to that shooting. Denver City Clerk Paul Lopez said in a posting on Twitter that his offices in the city’s Webb building were damaged.

After the shooting, one victim of the shooting at 20th and Market called for help from Blake Street and then went to a hospital on his own, police said, and investigators believe other innocent bystanders may have been shot.

Denver public safety director Armando Saldate lauded police officers who, on video surveillance showing the shooting, can be seen running “without hesitation” to victims, “rendering care immediately — life-saving care.”

According to the nonprofit Gun Violence Archive, there have been 291 mass shootings in the United States so far this year. Gun violence deaths overall had reached 19,161, the archive data drawn from law enforcement agencies showed.

In Denver, a celebratory parade is planned for Thursday morning downtown featuring Nuggets basketball players on floats.

“There is certainly the potential for danger any time there is a large gathering,” Thomas said. “There are far too many guns in our community today. … I know there was celebratory gunfire throughout the city.”