An overnight brawl between two groups of students escalated into violence Friday when a freshman at Northern Arizona University opened fire on four fraternity members, killing one and wounding three.

Steven Jones, an 18-year-old fraternity pledge, told police he shot the group of students only after they hit him in the face and chased him, according to court documents. He also said he tried to administer first aid to one of the victims.

Prosecutors said the suspect's account amounted to a "self-serving" statement and alleged Jones was the aggressor.

"There is no indication of self-defence here," Deputy County Attorney Ammon Barker said. "The defendant had retreated from the fight, he obtained a gun and then he went back into the fray."

The shooting occurred in a parking lot just outside Mountain View Hall dormitory on the Flagstaff campus, which provides housing for many of the campus' sororities and fraternities. Several frantic people called 911 to report the shooting, some looking down onto a parking lot from their dorm windows and seeing people with gunshot wounds.

"I first thought it was a joke but people started screaming," said one man, breathing heavily on the phone.

Dispatchers instructed some callers to stay inside, lock their doors and turn off the lights while advising help was on the way.

The victims were all members of the Delta Chi fraternity while Jones was a pledge at Sigma Chi. It's not clear why the fight started.

'Our hearts are heavy'

Student Colin Brough was killed, and Nicholas Prato, Kyle Zientek and Nicholas Piring were wounded. The prosecutor said Brough was hit twice — in the chest and shoulder — with Jones's .40-calibre handgun. Flagstaff Medical Center said it couldn't release any information on conditions.

"This is not going to be a normal day at NAU," said school President Rita Cheng. "Our hearts are heavy."

Jones told investigators that several people approached him and two friends while they were outside a residence. A fight broke out between the two groups, and Jones said he was hit in the face. He says a group chased him to his car, where he retrieved a handgun. Two of the victims had stopped following him but turned around when Jones yelled that he had a gun, court documents said.

Northern Arizona University Shooting

Steven Jones, 18, has been charged with first-degree homicide and three counts of aggravated assault. (The Associated Press)

At one point, a group tried to subdue Jones, who fired a shot in the air. Jones said he then dropped his firearm, which had a flashlight attached to it.

Jones was booked Friday for one count of first-degree homicide and three counts of aggravated assault.

Defence attorney Burges McCowan asked Flagstaff Justice Court Judge Paul Christian to allow Jones to be released to his parents in Glendale, Ariz., saying he has no prior criminal history and is a lifelong resident of Arizona. The set bond at $2 million.

"He has no other place to go," McCowan said.

'The happiest person'

Brough was from Castle Rock, Colo., about 48 kilometres south of downtown Denver. He loved to play lacrosse and wanted to be successful so he could help other people, said his cousin, Ryan Jernegan of Woodbury, New Jersey. He also worked as a lifeguard at a Flagstaff recreation centre.

"He was the happiest person that you probably would ever meet," Jernegan said.

He worked as a cashier at the Puma outlet store in Castle Rock during the summer after graduating high school. Manager Chauncey Musser remembered him as an outgoing employee with a seemingly bottomless supply of energy.

Alex McIntosh, a friend of Zientek, said he worked part time at the High Country Conference Center while attending school full time.

"He's very calm, very respectful, has a great manner, calm demeanour and you'd never expect him to be caught up in something like this," McIntosh said.

Panic on campus

The shooting set off panic at the Flagstaff campus as students heard gunshots and quickly took to social media to figure out what happened.

Student Maria Gonzalez told The Associated Press that she at first suspected firecrackers when the shooting happened.

"I was studying for an exam, so I looked out the window and see two people running, and that's when I realized they weren't fireworks, they were actually gunshots," she said.

The Flagstaff shooting comes on the same day that President Barack Obama visited Roseburg, Oregon, where eight students and a teacher were shot and killed last week at Umpqua Community College.

In Texas, a student was killed and another person was wounded in a shooting outside a Texas Southern University student-housing complex on Friday. A brief panic broke out in Kentucky hours later when there were reports of shots fired on a college campus. The reports turned out to be unfounded.

Northern Arizona University Shooting

A member of the Northern Arizona University police department talks on a cellphone after a campus shooting. (Jake Bacon/Arizona Daily Sun/Associated Press)

Northern Arizona University is a four-year public university that has more than 25,000 total undergraduate students at the campus in Flagstaff, a city about two hours north of Phoenix that is surrounded by mountains and ponderosa pines. The city of 70,000 people has a reputation for being a safe place and typically records only one murder per year.

"It's crazy. You don't think this stuff happens. When I think of Flagstaff, I think safety," said freshman Cameron Sands, who had pledged at a fraternity and was supposed to move into Mountain View Hall on Friday.