At least five people are dead, including the suspected gunman, following a shooting at a church in Sacramento, California, on Monday, authorities said. 

The gunman killed his three kids before turning the gun on himself around 5 p.m. at an Arden-Arcade area church in Sacramento. Those killed were pronounced dead at the scene and authorities believe the incident was domestic violence-related. The fifth person who died was described as an adult. 

"We are actively monitoring the shooting at a church in Sacramento and working closely with local law enforcement," tweeted the Office of California Governor Gavin Newsom. "Our thoughts are with the community, parishioners, and all those impacted by this horrific event."

Law enforcement is investigating, and nearby roads were closed after the incident. 

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"Howe and Ethan and Howe and Cottage have a large police presence due to a shooting, please avoid the area," Sacramento County Sheriff's Office wrote on Twitter. "The Sheriffs Office PIO will be at the command Post located at the Home Depot on Howe and cottage."

A massive law enforcement presence was at the scene, including a SWAT vehicle, according to videos posted by local media on Twitter. They included officers from the Sacramento Police Department, the Sacramento County Sheriff's Office, and the California Highway Patrol, Sacramento's KXTV-TV reported

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The three children killed in the shooting were under the age of 15, said Sgt. Rodney Grassmann, a spokesman for the sheriff’s office. The shooting was contained inside the church. Grassmann said, and the identifies of those involved have yet to be released.

The sheriff's office said the father had a restraining order against him and the incident occurred during a supervised visit with his kids at the church, where they would often meet, tweeted Morgan Rynor, a political anchor for KXTV-TV.  

The fourth person killed was an adult who was supervising the visit, Sheriff Scott Jones told reporters. It was unclear if that victim was a church employee or a social worker.

The shooter was not supposed to have a gun and the mother of the three kids has been notified, Rynor added.

Sacramento City Councilman Eric Guerra deemed the incident a "mass casualty shooting event," on Twitter. He advised people in the area to be on alert as local law enforcement responded. 

Gov. Gavin Newsom also weighed in on the shooting via Twitter, calling it a "senseless act of gun violence in America - this time in our backyard. In a church with kids inside."

"Absolutely devastating. Our hearts go out to the victims, their families, and their communities. We are working closely with local law enforcement," Newsom tweeted.

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A church district leader said the victims were the shooter's daughters, and the shooter may have suffered from a form of mental illness, according to a tweet from Los Angeles Times reporter James Queally.

This is a developing story.

Editor's note: This story discusses suicide. If you or someone you know is having thoughts of suicide, please contact the National Suicide Prevention Lifeline at 1-800-273-TALK (8255).