A gunman has killed 12 people and injured four others when he indiscriminately opened fire in a municipal building in Virginia Beach, US.

DeWayne Craddock, described by law enforcement as “disgruntled” government employee opened fire “indiscriminately” upon his colleagues on Friday afternoon.

He was later killed by police.

Here The Independent looks at what we know so far about the massacre.

What do we know about the shooting?

The shooting happened shortly after 4pm on Friday afternoon when city employee DeWayne Craddock entered a Building two of the Virginia Beach’s Municipal Center wielding a .45 calibre handgun with a “sound suppressor”.

Situated next door to city hall, the the facility has office space for more than 400 employees and houses information technology, public works, planning and utilities departments.

The first victim was shot in a vehicle outside the public works and utilities building at the city municipal centre.

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The suspect then entered that building and “immediately and indiscriminately fired upon all the victims,” according to police chief James Cervera.

Police entered the building and got out as many employees as they could, then exchanged fire with Craddock.

He then engaged in a “long gunbattle” with four officers inside the building.

Mr Cervera emphasised that the crime scene is “most horrific” and “can best be described as a war zone”.

How many people were killed?

Eleven people were killed in the initial attack. A twelfth died on the way the hospital.

Four others were wounded, including a police officer whose bulletproof vest saved his life.

Was the suspect caught?

He died in the shooting. Mr Cervera said the officers shot the suspect, then gave him first aid, but he didn’t make it.

Who was the gunman?

DeWayne Craddock has been named as the one and only suspect in the shooting.

Mr Cervera said he would mention the name only once.

“Then he will be forever referred to as the suspect because our focus now is the dignity and respect to the victims in this case and to their families,” he said.

He added that the longtime public utilities employee was “disgruntled” with his employer.

What was the motive?

Mr Cervera declined to say more about what may have precipitated the attack.

“We have more questions than we really have answers,” he told reporters about two hours after the shooting.

How was the public reaction after the shooting?

The shooting sent shock waves through Virginia's largest city which is a popular holiday spot in the south-east of the state.

The shooting was believed to be the deadliest act of workplace gun violence in the United States since February, when a factory worker shot five colleagues to death in Aurora, Illinois, just after he was let go from his job.

“This is the most devastating day in the history of Virginia Beach,” Mayor Bobby Dyer said at an evening news conference.

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Virginia governor Ralph Northam said in a statement he was devastated by the “unspeakable, senseless violence” and is offering the state's full support to survivors and relatives of the victims.

“That they should be taken in this manner is the worst kind of tragedy," the governor said during the news conference.

The White House said Donald Trump had been briefed and was monitoring the situation.