The deadlock reached its climax when the man was shot through the windscreen of the vehicle following tense negotiations with specialist officers.

Dallas police tweeted the gunman was confirmed dead after a bomb robot with a camera was deployed to inspect the van.

TV footage showed the van had caught fire, with police saying it was due to the explosives inside.

Dallas Police Chief David Brown said James Boulware drove his armoured van, which was fitted with gun ports on the side, to the Jack Evans Police headquarters, planting bombs and opening fire with an automatic weapon.

He shot at the building from a number of different vantage points blasting giant holes in the glass front and narrowly avoiding killing an officer.

Police Chief Brown said one officer had been saved by a can of Coke. The officer had left his post to get a drink and had he not done so he would have likely been shot, he said.

After launching the attack Boulware, who was arrested in 2013 after threatening to attack schools and churches, fled the scene, leading officers on a car chase through the streets of Dallas, during which he rammed a police cruiser and repeatedly fired on officers.

Scenes of the chase were caught on camera by members of the public. At one point the armoured vehicle is seen driving straight at a police officer's car under a hail of gunfire. The officers are pictured fleeing from the scene.

In another video, posted on social media, a police officer is seen approaching the van before back up vehicles arrive and a volley of gunfire is heard.

The vehicle was finally surrounded in a car park where the SWAT unit was sent in to negotiate with Boulware, who has a history of domestic violence, and said he had blamed police for losing custody of his son and "accusing him of being a terrorist". 

As the stand-off played out Dallas police discovered two pipe bombs outside the Dallas Police Department headquarters and increased security at all police facilities. 

One was discovered in a bag underneath a police vehicle and exploded when a police robot attempted to move it. 

The police department has released pictures of bullet holes in the windows of the headquarters and of the damage done by automatic weapon fire to a police vehicle.

Boulware had been arrested by police in 2013 after it was alleged he tried to choke his mother before threatening to kill members of his family and launching attacks on churches and schools.

When officers raided the home of the former mechanic they found four or five long guns, three or four pistols, tubs of ammunition and body armour.