MILWAUKEE (CBS) — Six people were killed Wednesday afternoon, including the gunman, in a shooting at the Molson Coors brewing campus in Milwaukee.

The shooting happened in a brewery inside the Molson Coors plant, better known as the Miller brewery, at 4000 W. State St.

Milwaukee Police Chief Alfonso Morales said officers arrived at the plant 2:08 p.m. for a call of a shooting. They found a 51-year-old Milwaukee man, who was believed to be the gunman, dead of a self-inflicted gunshot wound, Morales said.

There were five more adult victims – all of whom were employees at the plant, Morales said. Late Wednesday, Morales said the victims had been identified, but the identities will not be released until at least Thursday.

Milwaukee police sources told CBS 2’s Jermont Terry that the gunman was fired earlier in the day. He returned and started shooting with a silenced gun, police sources said. Sources also said the gunman appeared to have stolen the nametag of another employee when he returned to work with a gun.

But a subsequent email release from Molson Coors described the gunman as an “active brewery employee.”

Sources told CBS 2 that at the time of the shooting, the plant was in the middle of a shift change. The plant was placed on lockdown and everyone was told to find a safe place to hide.

One person who was talking to CBS 58 Milwaukee in the mid-afternoon reported being locked in a closet, and did not expect to go anywhere anytime soon.

Police officers and firefighters responded to the scene wearing ballistic gear, CBS 2 Investigator Megan Hickey reported.

Around the perimeter of the MolsonCoors campus, members a Milwaukee Police SWAT team were standing guard.

By 4:44 p.m., there was no further active threat, Milwaukee Police said. By 9:40 p.m., the scene was secured and all employees who had been in the building were accounted for and had been evacuated.

But as late as 6:30 p.m., some employees were still in the building.

“There’s over 1,000 employees. There’s multiple buildings – more than 20 buildings we have to secure. We have checkpoints that we’re checking off each employee one by one. That’s going to take several hours to do,” Morales said at that time.

MORE: Public Officials React With Shock And Grief To Molson Coors Brewery Shooting In Milwaukee

The most difficult task remains in recovering the bodies.

Milwaukee Mayor Tom Barrett said it was a tragic day for the city and the state of Wisconsin.

“There were five individuals who went to work today, just like everybody goes to work, and they thought they were going to go to work, finish their day, and return to their families,” Barrett said. “They didn’t, and tragically, they never will.”

Barrett also noted that the brewery has been part of the Miller family and the city of Milwaukee for 165 years, and this is the worst thing ever to transpire there.

Milwaukee Ald. Russell Stamper (15th), whose district includes the plant, called the situation “super sad.”

“It’s a horrible situation, and I’m just here to see what I can do and handle support,” Stamper said. “It’s just sad.”

Wisconsin Lt. Gov. Mandela Barnes lamented that mass shootings happen with such frequency in the U.S. He said this the 11th mass shooting since 2004.

“This is seething that we should never come to accept in society,” he said.

Wisconsin Gov. Tony Evers said the shooting was an attack on and a tragedy for the whole state.

“The first lady and I will be praying tonight together for the lives that have been lost. It is a tragedy for Milwaukee, yes, but it is a tragedy for the entire state of Wisconsin,” Evers said. “Wisconsin is a strong state. What happens in Milwaukee impacts people all across the state from Cornucopia to Kenosha.”

Molson Coors President and Chief Executive Officer Gavin Hattersley came to Milwaukee in support of the victims and their families.

“Were’ a family here at Molson Coors in Milwaukee, and this is an unthinkable tragedy for us,” he said late Wednesday.

Molson Coors is one of the city’s biggest employees.

The Molson Coors plant is one of the most popular tourist attractions in Milwaukee. Tours of the building were in progress at the time and were also placed on lockdown, CBS 58 Milwaukee reporter Bill Walsh reported.

Anastasia Vargas, who lives down the street, said she was leaving a doctor’s office nearby when she saw police officers racing to the scene of the shooting, and closing off nearby streets.

“It’s crazy. Milwaukee is getting real crazy. It just needs to stop. So much violence in Milwaukee. Too many kids around. I know over there there’s plenty kids around that area, and I just pray that everybody’s safe,” she said.

The Miller Valley, as the campus is known, employs about 1,400 people. That includes the cooling facilities known as Miller Caves, the plant itself, and offices.

The site is a mile and a half north of Miller Park and 1.7 miles west of Marquette University, CBS 2’s Chris Tye reported. Police were blocking streets and access at 35th Street and Wisconsin Avenue.

As of just before 3:30 p.m., CBS 58 Milwaukee reporter Brendan Cullerton reported the Miller Valley area where the plant is located was blocked off.

Nearby businesses and schools were also placed on lockdown.

“I’m happy they were able to let me get him. I guess they’re not realty releasing the other kids if their parents aren’t here to get them yet. So I’m just glad I was able to get here on time, get him home, get him out of here, and just kind of get him away from the area for now,” parent Ryan Hall said as he arrived at the school to pick up his son.

“All of us were just kind of in shock because we didn’t know what was going on,” Hall’s son said.

Parents were advised to stay away from area schools until it was safe.

“I can’t even come here at first – this is all blocked off,” said parent Natasha Williams.

She said the circumstances left her “scared, and not knowing – and they said it’s an active shooter, so that’s serious.”

“They told me to go to the coat closet to hide, but then, when it was a code yellow, they told me to go in the auditorium, and wait for our buses and our moms,” said Williams’ son, Mario.

Terry also talked with the mother of a man who works on the corporate side at Molson Coors. That employee was told to hide out underneath his desk – it was not clear whether he had been able to leave as of 6 p.m.

The FBI and the Bureau of Alcohol, Tobacco, Firearms, and Explosives was on the scene in addition to Milwaukee Police and Milwaukee County Sheriff’s Police, CBS 58 reporter Brittany Lewis reported.

Before Wednesday, the last mass shooting in the Milwaukee area was on Aug. 5, 2012, at a Sikh temple in suburban Oak Creek.

That day, Wade Michael Page, 40, walked into the Sikh gurdwara – or house of worship – armed with a 9mm handgun, and opened fire on worshippers without saying a word.

Six of his victims died, and three others were critically wounded, including a police officer who responded to the shooting. Authorities said Page ambushed a responding officer, shooting him at least eight times, then opened fire on a second officer, who returned fire and killed Page.

Page was a U.S. Army veteran, and a former leader of a white supremacist heavy metal band.