Snipers shot killed five police officers and wounded six more during a protest against police brutality in Dallas, in what US President Barack Obama called a “vicious, despicable and calculated” attack.

A suspect who engaged in gunfire with the police reportedly killed himself, although some local media outlets said he had shot himself. Three more suspects including a woman were arrested, Dallas Police Chief David Brown said early on Friday morning.

The suspect who reportedly died warned negotiators there are “bombs all over” and the “end is coming”, prompting police to place the city on lockdown while they conducted “extensive” sweeps of the city center amid reports of bombs planted downtown.

US aviation authorities restricted flights over Dallas after the deadly shooting, which took place at around 8.45 pm on Thursday. The police chief said the snipers fired “ambush style” upon the officers.

Just after the shootings, the police had tweeted a photo of one of the suspects and appealed for information on him. They later said in a statement that the suspect had surrendered. Reports suggest that person has been released.

The shootings, which police described as a “terrorist incident,” sparked chaotic scenes of people running for their lives during a march by several hundred demonstrators to protest the fatal shootings this week of two black men by police elsewhere in the country.

It was the biggest single loss of life for law enforcement in America since the September 11, 2001 attacks, and appeared likely to further strain already tense race relations in the country.
The gunshots in Dallas came amid protests nationwide over the recent police shootings. (AP Photo)

The protests in Dallas were among several across the country that were held after a Minnesota officer on Wednesday fatally shot Philando Castile while he was in a car with a woman and a child in a St Paul suburb. The aftermath of the shooting was live-streamed in a widely shared Facebook video. A day earlier, Alton Sterling was shot in Louisiana after being pinned to the pavement by two white officers. That, too, was captured on a cellphone video.

Video footage from the scene showed that protesters were marching along a street in downtown, about half a mile from City Hall, when the shots erupted and the crowd scattered, seeking cover.

Mr Brown said that it appeared the shooters “planned to injure and kill as many officers as they could.”

“In times like this we must remember – and emphasize – the importance of uniting as Americans,” said Texas Governor Greg Abbott.