Police have arrested three suspects over the Dallas police shootings.

Three suspects are now in custody while a fourth person is involved in a shoot-out with police, Dallas Police Chief David O. Brown has said.

As they were detained, they are said to have told officers: 'The end is coming... and there are bombs all over the place.' 

Read more: Dallas police shootings: Snipers kill five US officers during march against American police shootings of black men

Police previously one of the snipers was protester Mark Hughes, whose picture police circulated on social media in a bid to find him in downtown Dallas. He has now been released. 

Snipers opened fire shooting 11 police officers manning a protest over the death of two black America men by police. 

Five US officers have been confirmed dead while three more remain in critical condition.

A member of the public was also shot.

The bomb squad was checking out a suspicious package discovered after the shootout, police said.

Brown said Dallas police had contacted the FBI and the federal Bureau of Alcohol, Tobacco, Firearms and Explosives “to help us search for both these suspects — or maybe it’s more — and to do a very thorough search of this area where we believe there might be a bomb planted.”

Marchers protesting police shootings were moving down Lamar Street near Griffin when shots were fired.

One witness told The Dallas Morning News that he heard "what sounded like six to eight shots."

A bystander who was at the scene told WFAA the shooter stood by as the rally passed him, then opened fire on officers.

Another bystander, Richard Adams, said the protest was "a lovely, peaceful march," until they were walking down Commerce Street near the Bank of America building parking garage when he heard what sounded like "a bunch of firecrackers going off."

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"Everybody just stopped — 'Run, run for your lives!' Women with children and babies and everybody was chaotically running. And then, maybe I was a half-a-block away, calming down a little bit when we heard it again. [...] There must have been five times tonight — whenever we thought we were safe, people said 'Run, people were shot!'"

The protesters had gathered after a Minnesota officer on Wednesday fatally shot Philando Castile while he was in a car with a woman and a child in St Paul.

The aftermath of the shooting was purportedly livestreamed in a widely shared Facebook video.