Three people were fatally shot, and 15 others were hurt, after an altercation broke out at a park in the desert city of Las Cruces, police said on Saturday.
Police and fire crews arrived at just after 10pm on Friday to a chaotic scene at Young Park, where an unauthorised car show had drawn about 200 people, police said in a news conference.
Gunshot victims ranging in age from 16 to 36 were treated there or taken to hospitals.
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Between 50 and 60 handgun casings were scattered across a wide swath of the park, Police Chief Jeremy Story said, suggesting multiple shooters and multiple weapons among two groups whose "ill will" toward each other are believed to have led to the shootings.
Several others were injured in the crossfire, he said.
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The dead were identified only as a 16-year-old boy and two men, ages 18 and 19, police said.
Their names and those of the other victims were not yet being released.
Local police were being assisted in their investigation by New Mexico State Police, the Doña Ana County Sheriff's Office, the FBI and the federal Bureau of Alcohol, Tobacco, Firearms and Explosives.
Las Cruces Fire Chief Michael Daniels said 11 patients were sent to three local hospitals or to University Medical Center of El Paso, the regional trauma centre.
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As of Saturday, he said, seven victims were in El Paso, four had been treated and released and the conditions of the other four were not known.
Authorities are seeking video from the park and tips from those present as they work to identify a suspect or suspects.
"This horrendous, senseless act is a stark reminder of the blatant disregard people in New Mexico have for the rule of law and order," Story said.
He vowed that authorities will find everyone responsible and said, "We will hold them accountable to the criminal justice system."
Story acknowledged that illegal car shows at Young Park are not uncommon and that the police presence has been larger in the past.
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Understaffing on Friday, he added, meant that he had "no units available for most of the night."
In an Instagram post on Saturday, City Councilor and Mayor Pro Tem Johana Bencomo expressed grief over the shootings.
"Part of me wanted to write that this is something you never really think this is going to happen in your city, but that actually feels deeply untrue," she said.
"Honestly now days a tragedy like this feels like a nightmare just waiting to come true at any possible moment, yet also always praying and hoping it never will."
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Mayor Eric Enriquez called for people to support the victims, their families and the community after the "senseless" event.
"We need to stand strong. We need to come together," he said.
Police were still on the scene on Saturday, and the area around the park was closed to traffic, according to local media reports.
"This is a huge crime scene with a lot of moving parts," Story said. "It will take time to process it thoroughly and reopen everything."
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In the New Mexican capital, Santa Fe, the state Senate held a late-night moment of silence as word of the shootings spread.
The shootings cast a pall over efforts by Governor Michelle Lujan Grisham and the state Legislature to find effective solutions to persistently high crime rates and concerns about gun violence.
Lujan Grisham said she was gripped by sorrow for victims' relatives as well as anger and disappointment that more public safety bills did not make it to her desk before the legislative session closed at noon on Saturday.
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"We don't have sufficient tools, we are not bringing accountability to these communities," she said at a news conference.
"I'm so sorry for the individuals whose lives are forever changed, for a community that will be shattered."
Lujan Grisham recently signed off on a package of enhanced penalties for vehicle theft, fentanyl trafficking and school-shooting threats, along with a ban on devices that convert guns to automatic weapons.
Legislators passed an overhaul of the state's red-flag gun law, under which firearms may be temporarily removed from people who may pose a danger, and bolstered funding for addiction and mental health treatment.
But the governor excoriated legislators for a lack of progress on juvenile justice reforms and highlighted the apparent large number of weapons used in the Las Cruces shootings.
"These tragedies have to end," she said. "The amount of guns that find their ways into public parks and schools and churches and grocery stores and parties and cars must end."
Las Cruces sits on the edge of the Chihuahuan Desert along the Rio Grande in southern New Mexico, about 70 kilometres from the US-Mexico border.
