A dad killed his three daughters and an adult with them before turning the gun on himself at a church in California, it is reported.
The children tragically shot were aged 9, 10 and 13, said Sargeant Rod Grassman of the Sacramento County Sheriff’s Office.
“This was not a random shooting,” he said, saying those involved “all knew each other.”
Police are investigating after the man carried out the shootings when he walked inside The Church Sacramento, in the Arden-Arcade neighbourhood of Sacramento, northern California.
The attack took place just after 5pm local time on Monday.
The fifth person who was shot dead was identified as a supervisor or chaperone, said Sacramento Metropolitan Fire District Capt. Parker Wilbourn.
The man is believed to have had a restraining order, and the mother of the children, who was not present, was later contacted by police.
A SWAT team was dispatched to the church after someone upstairs in the building heard the shooting and police urged local people to avoid the area.
A call was made to emergency services at 5.07pm reporting a shooting inside the church after a worker upstairs in the building heard a single gunshot followed by several more shots, reported CNN.
A dead body was seen being taken out of the church at around 6.30pm, with a helicopter also reported to arrive at the scene around that time.
There were other people inside the church at the time of the shooting although it is not known if there was a service taking place, but no one else was injured.
A statement on Twitter from the Sacramento Sheriff read: "Howe and Ethan and Howe and Cottage have a large police presence due to a shooting , please avoid the area.
"The Sheriffs Office PIO will be at the command Post located at the Home Depot on Howe and cottage."
Another sheriff later described the incident as a "tragic domestic violence case".
A statement from the office of California Governor Gavin Newsom said: "We are actively monitoring the shooting at a church in Sacramento and working closely with local law enforcement.
"Our thoughts are with the community, parishioners, and all those impacted by this horrific event."
Governor Newsom later called the shooting "another 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."