A municipal employee sprayed gunfire "indiscriminately" in a government building complex on Friday in the US state of Virginia, police said, killing 12 people and wounding four in the latest mass shooting to rock the country.

The shooter was also killed after an extended gun battle with responding officers, in a scene that "best could be described as a war zone," Virginia Beach police chief James Cervera told a news conference.

The shooting happened just after 4pm (20.00 GMT), when the gunman entered one of the buildings at the Virginia Beach municipal complex and "immediately began to indiscriminately fire on all of the victims," Cervera said.

One victim was killed outside in his vehicle, while the others were found on all three floors of the building. Police upgraded the casualty toll to 12 dead and at least four wounded Friday night, after earlier reporting 11 dead and six wounded.

The shooter was armed with a .45-caliber handgun fitted with a sound suppressor, and he reloaded multiple times with extended magazines, Cervera said. Unlike some states, silencers are legal in Virginia, though it is illegal to have one in Virginia Beach per local ordinance.

The four responding police officers "stopped this individual from committing more carnage in that building," he added.

Police unsuccessfully tried to resuscitate the suspect after he was shot, Cervera said. He further said that police had recovered “additional weapons” that were in the possession of the suspect.

The weapons were recovered at the scene as well as at the home of the suspect, identified as Dewayne Craddock.

Authorities said that the suspect was a longtime employee of the public utilities department.

The wounded included a police officer, who was saved by his bulletproof vest. All were undergoing surgery on Friday night.

'Surreal'

The building where the shooting took place in Virginia Beach -- a city of 450,000 people about 200 miles (320 kilometers) southeast of Washington -- housed the city's public works and utilities offices and can have 400 people inside at any time.

"This is the most devastating day in the history of Virginia Beach," Mayor Bobby Dyer told reporters. "The people involved are our friends, co-workers, neighbors and colleagues."

Megan Banton, a public utilities employee, told local television station WVEC that during the chaos she and about 20 coworkers hid in an office, where they used a desk to wedge the door shut.

"We just wanted to try to keep everybody safe as much as we could and just trying to stay on the phone with 911, just because we wanted to make sure (police) were coming. They couldn't come fast enough," she said, adding that it felt like "hours."

"We heard gunshots. We kept hearing gunshots and we kept hearing the cops saying, 'Get down.'"

Banton said it felt "surreal" to have a mass shooting in her office building, and having survived it she just wanted to go home and hug her family.

"I have an 11-month-old baby at home and all I could think about was him and trying to make it home to him," she said.

150th mass shooting

President Donald Trump had been briefed on the shooting and was monitoring the situation, the White House said.

According to the Washington-based Gun Violence Archive monitoring group, Friday's shooting was the 150th mass shooting in the United States this year, defined as a single event in which four or more people are shot or killed.

Despite the scale of gun violence across the nation, gun ownership laws are lax and efforts to address the issue legislatively have long been deadlocked at the federal level.

Among Democrats, the response to the shooting was especially pointed, with many of the party's White House hopefuls weighing in on the gun violence crisis.

"Another horrific shooting shocks the nation, this time in Virginia Beach," Pete Buttigieg tweeted. "Already, this much is clear: it is unacceptable for America to remain the only developed country where this is routine. We must act."

'Horrific day'

Senator Bernie Sanders decried the influence of the National Rifle Association, a powerful lobby group that routinely calls for more guns in US society so that ordinary citizens are armed and ready to confront a "bad guy."

"Congress must listen to the American people and pass gun safety legislation. This sickening gun violence must stop," he said in a tweet.

Virginia Governor Ralph Northam said it was a "horrific day" for the state.

"Our hearts ache over the senseless violence that has been inflicted upon the Virginia Beach community today. My deepest condolences and prayers go to the families of those who left home this morning and will not return tonight," he said at a news conference.

Singer and music producer Pharrell Williams, a native of Virginia Beach, paid homage to the strength of his hometown.

"We are praying for our city, the lives that were lost, their families and everyone affected. We are resilient," he said in a tweet.

"We will not only get through this but we'll come out of this stronger than before we always do."A longtime, disgruntled city employee opened fire at a municipal building in Virginia Beach in the United States on Friday, killing 12 people before police fatally shot him, authorities said.

Six other people were wounded in the shooting, including a police officer whose bulletproof vest saved his life, said Virginia Beach Police Chief James Cervera.

Five patients were being treated at Sentara Virginia Beach General Hospital and a sixth was being transferred to the Trauma Center at Sentara Norfolk General Hospital, Sentara Healthcare tweeted.

The shooter opened fire in Building 2 of the municipal center, which is adjacent to City Hall. The building houses the city’s public works, public utilities and planning departments, according to City Councilwoman Barbara Henley, who arrived at City Hall building about 4pm on Friday just after the shooting.

Megan Banton, an administrative assistant who works in the building where the shooting happened, said she heard gunshots, called 911 and barricaded a door.

“We tried to do everything we could to keep everybody safe,” she said. “We were all just terrified. It felt like it wasn’t real, like we were in a dream. You are just terrified because all you can hear is the gunshots.”

She said she texted her mom, telling her that there was an active shooter in the building and she and others were waiting for police. Banton works in an office of about 20 people that is part of the public works department.

“Thank God my baby is OK,” Banton’s mother, Dana Showers, said.

Cervera identified the shooter as a disgruntled employee of the Public Utilities Department. He did not release his name.

Christina Pullen, a spokesperson for the FBI in Norfolk, said the bureau is assisting.