(CNN) Sacramento police are appealing for the public's help to find multiple shooters who opened fire downtown early Sunday morning, killing six people and leaving the California city with "a broken heart," according to the mayor.
In addition to the six dead, another 12 people were wounded at the scene near 10th and K streets, police said in a statement.
Officers responding to the sound of shots fired around 2 a.m. found a large group gathered, as well as gunshot victims, the statement said.
"Officers began life-saving measures to multiple victims on scene. Despite these efforts, six victims were pronounced deceased at the scene. Twelve other victims with varying degrees of injuries have also been located," police said.
Sacramento Police Chief Katherine Lester said the dead included three men and three women. The 12 wounded were being treated at area hospitals, she said in a news conference Sunday afternoon.
"Investigators are working to identify those responsible for this horrific act. We know that a large fight took place just prior to the shootings. And we have confirmed that there are multiple shooters," Lester said.
She said investigators were interviewing a number of witnesses and located hundreds of pieces of evidence from the scene, including a stolen handgun.
Lester thanked members of the public for sending in tips and video from the incident, some of which she said had also been captured by a nearby police camera.
"We are shocked and heartbroken by this tragedy but we are also resolved as an agency to find those responsible and to secure justice for the victims and their families," she said.
In an earlier statement, police said social media video appeared to show an altercation before the shooting.
They appealed to the public to send in any additional photos or videos.
California Gov. Gavin Newsom said his administration is monitoring the situation.
"What we do know at this point is that another mass casualty shooting has occurred, leaving families with lost loved ones, multiple individuals injured and a community in grief," the governor said in a statement.
"The scourge of gun violence continues to be a crisis in our country, and we must resolve to bring an end to this carnage."
"9th St to 13th St is closed between L St & J St as officers investigate a shooting with multiple victims," Sacramento police tweeted earlier. "Conditions unknown at this time. Please avoid the area as a large police presence will remain and the scene remains active."
Lester told reporters Sunday morning that a large crowd was gathered in the area when gunfire erupted but it was unclear whether the crowd was connected to a particular venue or event.
The shooting scene is within a few blocks of several notable landmarks: the California State Capitol, Sacramento City Hall and Golden 1 Center, where the Sacramento Kings are scheduled to play Sunday night.
"Our community grieves as we mourn those lost today senselessly killed by gun violence," the Kings said in a statement. "Our prayers are with those who have been wounded and (our) heart goes out to all the families in anguish affected by this devastating act."
Community activist Berry Accius told CNN affiliate KCRA that he arrived at the scene soon after the shooting.
"The first thing I saw was like victims. I saw a young girl with a whole bunch of blood in her body, a girl taking off glass from her, a young girl screaming saying, 'They killed my sister.' A mother running up, 'Where's my son, has my son been shot?'" he said.
At a news conference Sunday, Sacramento Mayor Darrell Steinberg shared his grief about the mass shooting.
"This morning, our city has a broken heart. This is a senseless and unacceptable tragedy, and I emphasize the word unacceptable," Steinberg said. "Thoughts and prayers, of course are appropriate for the victims and their families. And the people who are still who are fighting for their lives now in the hospital. But thoughts and prayers are not nearly enough. We must do more as a city, as a state and as a nation."
Steinberg referred to the country's struggle with gun violence as a "sickness," and called for early intervention and prevention for young people. He said many of the victims' families had gathered at City Hall awaiting information.
Several city council members at the news conference issued appeals to the Sacramento community to share any information or videos recorded from the shooting.
"Words can't express my shock & sadness this morning," the mayor tweeted earlier. "The numbers of dead and wounded are difficult to comprehend. We await more information about exactly what transpired in this tragic incident."