One woman has died after a gunman shot seven people at a birthday pool party near the University of California, San Diego.
The suspect, Peter Selis, 49, shot four black women, two black men and one Latino man at an apartment complex before he was shot and killed by police.
Investigators do not yet know why Selis, who was white, opened fire, police chief Shelley Zimmerman told reporters.
Several victims underwent surgery, and others are in critical condition, she said. One man was taken to the hospital after he broke his arm running away.
Local resident Rikky Galiendes, 27, heard gunshots at around 6pm and went to look outside his sixth-storey apartment.
He spotted a man bleeding and running near the pool below. Mr Galiendes said he called out to ask if the man needed help when his roommate grabbed him, yanked him down and pointed towards a man sitting in a chair with a gun.
Mr Galiendes said: "When we looked over the balcony, he was just sitting down with a gun on his lap.
"He was calm, you know? I mean from my perspective, the guy was ready to do whatever he was going to do. He shot at people having a good time and having a party."
Mr Galiendes and his roommate ran back inside and called police.
A police helicopter arrived first, and the pilot reported seeing multiple victims on the ground and that Selis appeared to be reloading in the pool area, Ms Zimmerman said.
Three officers arrived and shot Selis after he pointed a large-calibre handgun at them, she said.
Police believe Selis and one of the partygoers lived in the complex, police said.
"This is truly a horrific act of violence that took place here today," San Diego Mayor Kevin Faulconer said at a 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."
Mr Galiendes and his roommate stayed indoors until neighbours said it was safe to come out. He said the scene was horrifying.
"As soon as I heard the gunshots, I had goosebumps and the whole thing was really emotionally draining - seeing blood everywhere, seeing bodies on the ground, hoping they survived, seeing bloody footsteps, you know, of people who ran away. There was just so much blood. It was so surreal."
Mr Galiendes, a student at UC San Diego, said he has lived in the complex in the upscale San Diego community of La Jolla since September.
"It was chilling," he said.
"La Jolla is known to be really safe, and this is a family neighbourhood."