Two of the injured people were in critical condition but no one had died, interim Austin Police Chief Joseph Chacon said.

Gunfire erupted just before 1.30am on Saturday along 6th Street, a popular area filled with bars and restaurants. The street was barricaded to keep out vehicle traffic at the time of the shooting, Chacon said.

It was unclear what sparked the shooting.

Eleven of the injured people were taken to one local hospital, another person was taken to a different hospital, and the other person, Chacon said.

"Our officers responded very quickly," Chacon said.

"They were able to immediately begin life-saving measures for many of these patients, including applications of tourniquets; applications of chest seals."

Chacon also said some officers transported patients to hospitals in their police cruisers due to the nature of the scene, where it was hard to contain the crowd and get ambulances to those who were injured.

The shooter was not immediately arrested. Chacon said the description that police had of the suspect was "not very detailed," but said the person was believed to be a man.

Investigators were reviewing surveillance video and other evidence from the area, Chacon said.

Australian Associated Press