Victims of the Virginia Beach mass shooting included 11 municipal employees  – many of them co-workers of the “disgruntled” gunman – and one contractor.

Authorities have released the names of the people who died when the killer opened fire on a Virginia Beach city building on Friday.

“These are 12 individuals who came to work … thinking they would go home in the evening, and they didn’t return and it left a tremendous void in their families and in our community,” Virginia Governor Ralph Northam said.

The shooter, DeWayne Craddock, 40, who was employed as an engineer in the utilities department, was killed during a lengthy gun battle with police.

Four others hurt in the shooting were in hospitals Saturday – three of them critical – while an officer shot in the gunfight survived because of his ballistic vest.

The victims had worked for the city for between 41 years and 11 months and City manager Dave Hansen said they would “leave a void we will never be able to fill”.

Bodies were found on all three floors of the Virginia Beach building and in a car parked outside, according to authorities.

People gather for a public prayer service at Virginia Beach in the parking lot of a shopping center the day after a mass shooting. Photo: Getty

The victims were identified as Laquita Brown; Tara Gallagher; Mary Louise Gayle; Alexander Gusev; Katherine Nixon; Richard Nettleton; Christopher Kelly Rapp; Ryan Keith Cox; Joshua Hardy; Michelle Langer and Robert Williams.

Police said the gunman was armed with two .45 calibre pistols and used an employee pass to enter secure areas before firing “immediately and indiscriminately” on victims while reloading with multiple extended ammunition magazines.

At least one of the pistols was fitted with a “sound suppressor”, police said.

Both handguns were bought legally by the shooter within the past three years, Ashan Benedict, a special agent at the US Bureau of Alcohol, Tobacco, Firearms and Explosives, told the news conference.

Two more firearms were found at the home where Craddock lived alone, he said.

Meanwhile Virginia Beach police officers have been hailed heroes for stopping the shooter from inflicting “more carnage” after he stormed Building Two of the coastal city’s Municipal Centre complex at about 4pm local time.

Virginia Beach police chief James Cervera said he would only say the gunman’s name once: “Then he will be forever referred to as ‘the suspect.’”

The shooting is believed to be the deadliest act of workplace gun violence in the United States since February, when a factory worker killed five colleagues in Aurora, Illinois, just after he was retrenched.

FBI agents near building number 2 at the Virginia Beach Municipal Center, the scene of the mass shooting. Photo: Getty

Chief Cervera said the quick-thinking actions of the four police officers sent to the city building helped save the lives of potentially hundreds of terrified staff members inside.

DeWayne Craddock was killed after a drawn-out firefight with police. Photo: Twitter

The city building houses public works, public utility and a printing operation that collectively employ more than 400 people.

“Due to the sound of gunfire they were able to locate the floor on which the suspect was committing his carnage,” the chief said in a news conference.

“They immediately engaged with the suspect and I can tell you that it was a long battle between those four officers and that suspect.”

Among the people who received injuries was a police officer, who was shot at by the suspect and was saved only by his bulletproof vest.

“The suspect did shoot a police officer,” Chief Cervera said.

“Officers returned fire; [the] suspect is deceased.”

Virginia Beach police chief James Cervera said the event was “devastating”. Photo: AAP

“I want you to know that during this gun battle, basically the officers stopped this individual from committing more carnage in that building,” Chief Cervera said.

After apprehending the suspect, officers recovered a .45 caliber handgun with multiple extended magazines that were emptied at the time.

Police believe the suspect was reloading the extended magazines in that handgun before firing at staff in the building and at police officers.

“This devastating incident is going to change the lives of a number of families from our city,” Chief Cervera said.

FBI agents and Homeland Security Department forensic technicians are assisting local police due to the “size and scope and intensity” of the crime scene.

A girl leaves flowers at a makeshift memorial outside of the crime scene at Virginia Beach. Photo:Getty

One of the staffers inside the building, Megan Banton, told CNN of her horror as she and fellow colleagues scrambled to barricade chairs and desks against office doors upon hearing gunshots.

“We just heard there was an active shooter and we barricaded ourselves in offices to make sure we were all safe,” Ms Banton said.

“We kept hearing gunshots and we kept hearing the cops saying ‘get down’.”

Mayor Bobby Dyer said it was “the most devastating day in the history of Virginia Beach”.

“The people involved are our friends, co-workers, neighbours, colleagues,” Mayor Dyer said.

The mass shooting at Virginia Beach follows an earlier shooting incident on May 7 at a Colorado high school, in which two teenagers allegedly shot and killed a classmate and wounded eight others.

So far this year, there have been at least 10 mass shootings in the US, each one sparking public outcry and calls for tougher gun laws.