He walked inside and opened fire before shooting himself, police said.
The shooting happened within the Canterbury Manufactured Home Community, a mobile home park of some 470 trailers on the southeast side of town, near the Colorado Springs airport.
According to police, a birthday party was being held at the home when the boyfriend of a female victim arrived and killed the adults before taking his own life.
Seven people have been killed after a gunman opened fire at a birthday party at a trailer park in Colorado.
"My heart breaks for the families who have lost someone they love and for the children who have lost their parents", Colorado Springs Police Chief Vince Niski said in a statement.
The children were near where the shooting took place but were found unharmed. About a week before the shooting, there was another family gathering where there "was some sort of conflict" between the family and Macias, Niski said. A small group of adults stood nearby, some of them audibly sobbing, along with a small child. Police said there were no reported incidents of domestic violence during the relationship and that the shooter didn't have a criminal history. The families were connected through the marriage of Melvin Perez and Mayra Perez, who were present with their children.
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Islamic authorities estimated 90,000 people gathered for intense nighttime prayers at Al-Aqsa, the third-holiest site in Islam. Police patrols fired stun grenades as they moved through the area, and a police truck periodically fired a water cannon.
The Denver Post quoted neighbor Yenifer Reyes as saying she was awakened by the sound of gunfire and heard sirens before witnessing police take children out of the home and put them into a squad auto.
The massacre about 70 miles (110 km) south of Denver is the latest in a resurgence of mass shootings in the United States after such occurrences seemed to recede during the height of coronavirus pandemic restrictions.
As many as 10 people were killed at shooting in Boulder in March.
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The names of the victims will be released later, the statement said.
In a statement on Sunday, Colorado governor Jared Polis denounced the "terrible act of violence", noting it had taken place when "many of us are spending the day celebrating the women in our lives who have made us the people we are today".
Other bills advancing through the Democratic-led Legislature would tighten background checks, allow municipalities greater freedom to adopt gun control laws that are stricter than state law, and require a person facing a protection order related to domestic violence to report what firearms they possess.