Two people have died in an apparent murder-suicide at a Texas community college, prompting an active-shooter alert that instructed students and employees to barricade themselves into rooms.

President Barack Obama has said the shootings of five Dallas police officers would appear to have exposed "the deepest fault line of our democracy" but that Americans must reject such despair.

Military service changed suspected Dallas gunman Micah Johnson from an extrovert into a hermit, his parents have said.

The suspect in the deadly attack on Dallas police taunted authorities during two hours of negotiations, laughing at them, singing and at one point asking how many officers he had shot, the city's police chief has revealed.

An Army veteran killed by Dallas police after he fatally shot five officers amassed a personal arsenal at his home, including bomb-making materials, bulletproof vests, rifles, ammunition and a journal of combat tactics.

A suspect in the gun attack on police in the heart of Dallas told officers he was upset over recent police shootings of black men and wanted to kill white people, particularly police, according to officials.

Responsibility for the murder of five police officers in Dallas has been claimed by a radical civil rights group called the Black Power Political Organization.

The suspected gunman killed in a stand-off with Dallas police was an army veteran who served in Afghanistan.

Barack Obama has said the shooting of about a dozen police officers in Dallas was a vicious, calculated and despicable attack on law enforcement.

Update 3.49pm: A suspect in the gun attack on police in the heart of Dallas told officers he was upset over recent police shootings of black men and wanted to kill white people, according to officials.

Tornadoes that swept through the Dallas area have caused substantial damage, leaving at least 11 people dead and dozens of people injured.

Police in Dallas are reviewing how officers responded to a 14-year-old Muslim boy who brought a home-made clock to school that was mistaken for a possible bomb.

A downtown Dallas rally by presidential hopeful Donald Trump produced some of the sharpest scenes of conflict yet in his campaign as hundreds gathered to protest his positions on immigration and confronted supporters as they left the event.

Several men carrying automatic weapons opened fire on officers outside Dallas Police headquarters early today.

Thousands of demonstrators have rallied outside a Dallas primary school in protest over a white police officer’s actions against a mostly black group of teenagers at a pool party.

Two gunmen were killed after opening fire on a security officer outside a contest for cartoon depictions of Prophet Muhammad and a bomb squad was called in to search their vehicle as a precaution, authorities said.

The crane was eventually towed away.