Gunshots fired at Dallas police headquarters

Gunshots were fired at the police headquarters in Dallas, and a suspect has fled the scene in what witnesses said was as an armoured van.

As dozens of police cars gave chase, the man got involved in a stand-off in a car park, officials said.

"There has been an exchange of gunfire in the car park," officials added.

After the attack, police found suspicious bags near the headquarters. At least one contained explosives, prompting evacuations from areas around the police headquarters.

As an explosives robot approached one of them, it exploded, Maj. Max Geron tweeted. No one was injured.

Authorities believe up to four people may have opened fire from various locations with automatic weapons, including from the van, said Police Chief David Brown.

"There might be up to four suspects," Brown said.

The motive for the shooting is not yet clear. Dallas police say no police officers have been injured.