Five police officers killed in Dallas shooting

The shooting began near one of the busiest parts of the city's downtown, filled with hotels and restaurants.

Dallas Police Chief David Brown told reporters that two snipers fired 'ambush style' from an elevated position.

He said the police were negotiating with a suspect in the garage in downtown Dallas in the US state of Texas, hours after the violence erupted at a largely peaceful rally attended by hundreds of people.

Brown said the suspect has been exchanging gunfire with police over nearly an hour and was not being very cooperative in negotiations. He said plans were afoot to end the standoff.

According to the police chief, the suspects have threatened to have placed a bomb in the downtown area and that his department was coordinating with federal agencies.

During a press conference, Brown said the suspect has told negotiators that "the end is coming and he's going to hurt and kill more of us - meaning law enforcement - and that there are bombs all over the place in this garage and downtown."

There may be others out there. "We still don't have a complete comfort level that we have all the suspects," Brown said.

Brown said investigators are working under the assumption that all the suspects were working together.

He had initially said one of the suspects was arrested late last night after a shootout with the police. A suspicious package was found near him and has been secured by a bomb squad.

As the tragic shooting incident continued to unfold, US President Barack Obama was briefed about the incident, according to the White House.

Obama, who is in Warsaw for NATO Summit, earlier upon his arrival in the Polish capital said that the fatal shootings of black men by police this week in Louisiana and Minnesota were 'symptomatic of a broader set of racial disparities' and all Americans should be troubled by these incidents of brutality.

"All of us as Americans should be troubled by these shootings, because these are not isolated incidents. They're symptomatic of a broader set of racial disparities that exist in our criminal justice system," Obama said.

Citing statistics that showed black people were far more likely to be arrested and shot by police, Obama said African-Americans are 30 per cent more likely than whites to be pulled over. "After being pulled over, African-Americans and Hispanics are three times more likely to be searched."