LOS ANGELES－Four people, including a child, were shot and killed on Wednesday evening at an office building in Southern California, police said.

Police said they responded to reports of a shooting in the city of Orange around 5:30 pm local time and found "multiple victims at the scene including fatalities" where shots were fired.

Four people were pronounced dead at the scene and two others were transported to nearby hospitals, said the Metro City Fire Authority Dispatch, an emergency organization providing fire and emergency medical services to over 1.2 million residents in Southern California, including the city of Orange.

The shooting in California is the third such incident in the United States in weeks, with 18 people killed in two separate gun violence incidents in March.

The killings follow a mass shooting at a supermarket in Boulder, Colorado, last week that left 10 people dead. A week before that, six Asian women were among eight people killed in three Atlanta-area spas by a white gunman.

Video clips posted by the local ABC 7 news channel online showed the fatal incident occurred around a business complex in California, where at least two bodies were found outside the building, one on a second floor walkway, and the other in a courtyard.

There were also bloody clothes and what appeared to be a weapon on the scene as officers investigated.

A young woman told ABC 7 she heard two distinct sets of shots, one apparently the initial shooting and the other the gunfire exchange between the suspect and police.

"I was just in my room hanging out. All of a sudden I heard five to seven gun shots go off," the witness said. "And then I waited a couple minutes and the police came. And I heard a few more gunshots go off. It was a lot, quickly. Then the helicopter showed up and it was silent after that."

'Horrifying, heartbreaking'

In a tweet, Governor Gavin Newsom called the killings "horrifying and heartbreaking".

"Our hearts are with the families impacted by this terrible tragedy tonight," he wrote.

The shooter, whose motivations are so far unknown, sustained a gunshot wound and was taken to hospital, police lieutenant Jennifer Amat said, adding the suspect was in a critical condition.

People gathered outside the building after the shooting hoping to get word about loved ones.

Paul Tovar told KTLA-TV his brother owns a business there, Unified Homes, a mobile home broker."He's not answering his phone, neither's my niece," Tovar said. "I'm pretty scared and worried ... right now I'm just praying really hard."

Orange police said it was that city's deadliest shooting since 1997.

The city of Orange is about 50 kilometers southeast of Los Angeles and home to about 140,000 people.

Agencies - Xinhua