BROOMFIELD, Colo. — Police responded Thursday to what they said was an active shooting at an apartment building in the Denver suburb of Broomfield.

The police department released little information other than that officers had responded to gunshots at the Arista Flats apartments and that the area wasn’t safe.

The city’s SWAT team, crisis negotiators and law enforcement from nearby communities were assisting, police said. A school near the scene has been locked down.

In bystander video, authorities could be heard calling out to someone inside the apartment complex.

“This is the Broomfield Poice Department. Come outside with your hands up with no weapons. … Your mom wants to see you. Come out now,” an officer said.

Some people were evacuated and police sent out a reverse emergency notification to area residents to shelter in place.

Nate Schamel, who lives in an apartment building across the street from Arista Flats, told The Associated Press that he first heard sirens at around 6:45 a.m.

“I heard more and went outside onto my balcony. I saw a Broomfield Pd officer pull up across the street from me, get out with his rifle, cock it and start trotting down the street. I asked what was going on and he told me to go inside,” Schamel said in a text.

He said at 7:30, he called down to an officer who was next to his home and asked what was going on, and the officer told him and his wife to evacuate.

“This was after we had already heard multiple bursts of gunfire (from what sounded like multiple different weapons) and as we were leaving we heard 4-5 more bursts of gunfire,” he wrote.

Aaron Maxey, who also lives across the street from the Arista Flats complex, told Denver TV station KUSA that he heard 30 to 50 shots.

Broomfield is a city of about 75,000 people roughly 15 miles (24 kilometers) northwest of Denver.