Four people, including a child, were shot and killed Wednesday evening at an office building in Southern California, police said.
The shooter, whose motivations are so far unknown, was shot by an officer and taken to hospital, police said, adding that the suspect's condition was not known.
Police did not release any more information about the victims, but said that a fifth individual was hospitalized.
The incident began around 5:30 pm local time (0030 GMT) on the upper floor of a small office building in the city of Orange.
Police and the suspect exchanged fire, according to the Los Angeles Times.
"The situation has been stabilized and there is no threat to the public," the Orange Police Department said in a post to their Facebook page.
A Facebook livestream posted by a resident who lives near the office appeared to show officers carrying a motionless person from the building and officers providing aid to another person.
California governor Gavin Newsom posted on Twitter: "Horrifying and heartbreaking. Our hearts are with the families impacted by this terrible tragedy tonight."
"I'm deeply saddened by reports of a mass shooting in Orange County, and I'm continuing to keep victims and their loved ones in my thoughts as we continue to learn more," US Representative Katie Porter from California also tweeted.
The city of Orange is about 30 miles (48 kilometers) from Los Angeles and home to about 140,000 people. Orange Police Lt. Jennifer Amat said the shooting was the worst in the city since December 1997, when a gunman armed with an assault rifle attacked a California Department of Transportation maintenance yard.
Wednesday’s attack comes after two other high-profile mass shootings earlier this month, which set off a renewed debate about gun control measures in the United States.
On March 22, 10 people were killed in a shooting at a grocery store in Boulder, Colorado, less than a week after a man shot and killed eight people, including six women of Asian descent, at spas in Atlanta, Georgia.
