Gilroy Garlic Festival attendees scramble as gunshots are heard in the background. (Screengrab: Twitter/@wavyia)

Fifteen more were injured, including some who suffered gunshot wounds, although the number of those shot was not immediately clear. Some of them were hurt in the crush of bystanders trying to flee, according to police.

Police and ambulances raced to the scene of the incident, which happened on the last day of the Gilroy Garlic Festival, an annual three-day event south of San Jose.

Video posted on social media showed people at the event running for cover as shots rang out.

"Officers were in that area, and engaged the suspect in less than a minute. The suspect was shot and killed," Gilroy police chief Scot Smithee said.

A second person, "was involved in some way, we just don't know in what way," Smithee said. "We have no idea of a motive."

"What's going on?" a woman can be heard asking on one video. "Who'd shoot up a garlic festival?"

Aerial footage showed the festival grounds apparently deserted but with many emergency and police vehicles on surrounding streets and police in bullet-proof gear.

"It's just incredibly sad and disheartening that at an event that does so much good for the community had to suffer from a tragedy like this," Smithee said.

The gunman appeared to have cut through a fence to get into the annual Garlic Festival. He may have had one accomplice, Smithee added.

A city councilman told media earlier that one suspect had been taken into custody.

Councilman Dion Bracco told The New York Times: "They don't know if there were more, so they have to treat it as an active situation. We have police out here from as far away as San Jose."

Map locating Gilroy in California AFP/Kun TIAN

A witness named Julissa Contreras told NBC a white man in his 30s armed with a rifle opened fire indiscriminately.

"I could see him shooting in just every direction. He wasn't aiming at anyone specifically. It was just left to right, right to left," Contreras said, according to NBC.

NBC also reported that ambulance crew were told 11 people were "down" after the shooting.

Local hospital officials did not immediately respond to requests for comment.

"Be careful and safe!" US President Donald Trump wrote on Twitter.

Footage uploaded to social media appeared to show festival attendees scattering in fear and confusion as loud popping sounds could be heard in the background.

"What's going on?" a woman can be heard asking on one video. "Who'd shoot up a garlic festival?"

Evenny Reyes, 13, told the San Jose Mercury News that at first she thought the gunfire was fireworks. But then she saw someone with a wounded leg.

"We were just leaving and we saw a guy with a bandana wrapped around his leg because he got shot," Reyes told the newspaper. "There was a little kid hurt on the ground. People were throwing tables and cutting fences to get out."

Another witness, Maximo Rocha, a volunteer with the Gilroy Browns youth football team, said he saw many people on the ground, but could not be sure how many may have been shot and how many were trying to protect themselves.

He told NBC Bay Area that "quite a few" were injured, "because I helped a few".

One video posted on Twitter showed a blood-spattered woman sitting in the back of a semi-trailer and telling a man she had been shot in the hand.

Stage hand Shawn Viaggi told the Mercury News he heard gunshots and saw bullets hitting the ground. "I called out, 'It's a real gun, let's get out of here,' and we hid under the stage," Viaggi told the newspaper, adding that he saw police officers trying to resuscitate one man.

"The hearts of Gilroy PD and entire community go out to the victims of today's shooting at the Garlic Festival," the local police department tweeted.

Senator Kamala Harris, who is running for the 2020 Democratic presidential nomination, said: "Grateful to first responders who are on the scene in Gilroy and keeping those injured by such senseless violence in my thoughts."

Founded in 1979, the Gilroy Garlic Festival features food, drink, live entertainment and cooking competitions. It says it is hosted by volunteers and describes itself as the world's greatest summer food festival.

It was being held at the outdoor Christmas Hill Park, where weapons of any kind are prohibited, according to the event's website.

To provide a safe, family-friendly atmosphere, it said, entry was refused to anyone wearing clothing or paraphernalia indicating membership in a gang, including a motorcycle club./.

VNF/CNA