Seven people were shot, one fatally, when a gunman who witnesses said never left his poolside chair opened fire on a birthday party in an upscale apartment complex in San Diego late Sunday.

According to the San Diego Union-Tribune newspaper, police later shot and killed the suspect, identified as 49-year-old Peter Selis, believed to be a resident at the complex, which is in University City, a neighborhood near tony La Jolla.

A 2015 bankruptcy filing obtained by the Union-Tribune showed that Selis, who worked at a Ford dealership, faced massive debts.

A witness who saw the chaos from his apartment window told local TV station KGTV that the shooter appeared calm as he mowed down the victims.

“We could see the shooter sitting there with a beer in one hand and a gun in the other,” the witness, who was not identified, told the station.

“This is truly a horrific act of violence that took place here today,” San Diego Mayor Kevin Faulconer said at a late-night news conference. “Our entire city, all of our thoughts and prayers, all San Diegans’ thoughts and prayers, are with the victims and their families tonight.”

According to the Times-Union, authorities said the shooter was white and all the victims were people of color — four black women, two black men and one Latino man. The fatality, a woman, was not immediately identified.

At a news conference covered by local TV station KSWB, San Diego Police Chief Shelley Zimmerman said a police helicopter was the first law enforcement to arrive on the scene. The pilot saw the shooter appear to be reloading his handgun at the pool, Zimmerman said.

Three police officers then approached the pool area and shot Selis dead after he pointed his gun in their direction, the station reported. Zimmerman said the motive for the shooting remained unclear, and it was unclear whether Selis knew any of the victims.

Partygoer Drew Phillips told the Union-Tribune that shortly before the 6 p.m. shooting, a friend who was celebrating his birthday had approached Selis and offered him food and drink, which he declined.

“Six or seven minutes later it’s just pow, pow, pow, pow — out of nowhere,” Phillips told the paper. “...There was no indication that he was there to do evil.”

Phillips said he hopped a fence where he found a man he’d met at the party with a wound in his abdomen.

“He was just laying there, and just the look in his eyes — sheer terror,” Phillips told the paper. “I threw my phone down. I just picked him up and I just carried him. I basically ran as fast as I could with him in my arms.”

Another witness told KSWB that the gunman appeared to be "relaxed" during and after the shooting and was drinking a beer as the police approached the area.

Eight people — the seven shooting victims and a man who broke his arm in the confusion — were taken to hospitals. Several of the injured remained in critical condition, Zimmerman said Sunday night.

“Our hearts go out to all the victims, their families and anyone who witnessed this tragic event,” the chief said.