Shots were fired from an armoured van at Dallas Police headquarters early on Saturday before it drove away and was pursued by police, according to police and the Dallas Morning News.
The Dallas Police department said on its Twitter account the shooting was first reported at 12:27am local time and that witnesses said the suspects were inside an armoured car.
It was not immediately clear if anyone had been injured. The Dallas Morning News said dozens of police cars and SWAT personnel pursued the van, which it said was believed to be carrying explosives.
Police and the van then stopped on a nearby interstate highway, where officers were apparently negotiating with the driver, the paper said.
In a video on social media and also published online by local media, a police officer could be seen approaching a black van with a flashlight as two other police cruisers pulled up behind the vehicle.
The officer then abruptly turned and ran away and then a volley of gunshots could be heard.
In another video, the van could be seen ramming a police cruiser before gunfire rang out and the vehicle drove off. Further details were not immediately available.