A man opened fire at a family birthday party at a home in Colorado Springs in the early hours of Sunday morning, killing six people, including his girlfriend.
The shooter then killed himself, police said.
"Words fall short to describe the tragedy that took place this morning," Colorado Springs Police Chief Vince Niski said in a statement. "As the chief of police, as a husband, as a father, as a grandfather, as a member of this community, my heart breaks for the families who have lost someone they love and for the children who have lost their parents."
Children were inside the home at the Canterbury mobile home park when the shooting took place, but they were not injured.
The Colorado Springs Police Department said it first received a call about the shooting at 12:18 a.m. Upon arrival, police said, they found six adults dead and one person injured, who died shortly afterward in hospital. The names of those killed have not yet been released.
Police said that interviews with witnesses identified the boyfriend of one of the victims as the shooting suspect.
Research from Everytown for Gun Safety, an organization aimed at reducing gun violence, shows that on average, 57 women are shot and killed by an intimate partner in the US every month.
Its report on the links between gun violence and domestic violence showed that over half of mass shootings in the last decade involved a current or former partner or a family member of the shooter.
“The tragic shooting in Colorado Springs is devastating, especially as many of us are spending the day celebrating the women in our lives who have made us the people we are today," Colorado Gov. Jared Polis said in a statement Sunday, which was Mother's Day. "Multiple lives were taken today by this terrible act of violence. Families torn apart, and at a birthday party no less.”
Many tweeted at the governor in frustration at the lack of action on gun violence, particularly since Colorado has had multiple high-profile mass shootings. In March, a shooter killed 10 people at a Boulder supermarket.
The American Public Health Association says gun violence in the US is a public health crisis. It is the leading cause of premature death in the country, responsible for more than 38,000 deaths annually. As of May 7, at least 15,201 people have died from gun violence this year, according to data from the Gun Violence Archive.
Already this year, a number of shootings have targeted multiple members of a family. Last week, a man killed his parents, two police officers, and then himself during a shooting in North Carolina. In April, a former NFL player killed six people, including a couple and two of their grandchildren. A man in Brooklyn killed his daughter's mother and two sisters at a birthday party. That same day, six family members were killed by two brothers in Dallas who had made a murder-suicide pact.
"When these types of unspeakable acts happen, there is nothing that can be done to fully rebuild what was lost or replace those who are no longer with us," Niski, the Colorado Springs police chief, said Sunday.
Correction: A man killed his parents, two police officers, and himself in a shooting in North Carolina. A previous version of this story misstated the state.