Shooting at South Park Mall in San Antonio, Texas injures several

South Park Mall remains an active crime scene. Photo / Twitter

At least two gunmen have opened fire on a group of people at a shopping centre in San Antonio in the US state of Texas, injured four and sparking panic.

Police were called to the South Park Mall in the city's south just before 9pm local time in the wake of the incident.

San Antonio Police Department chief William McManus told reporters at the scene that two men opened fire before jumping into a black Dodge Charger vehicle and fleeing.

"It was barely inside the mall. There's a shallow breezeway on the far end of the entrance into the mall. It happened just inside that breezeway," Chief McManus said.

"The victims were just about to exit (the) mall. They were all together when they were shot, they were in one group."

He added that "many, a lot" of shots were fired, news.com.au reports.

Four people were, two of them in a serious condition, and rushed to a local hospital but they are all now stable.

The victims were three men aged 17, 26 and 41 and a woman aged 19 or 20.

Harrowing vision captured by an onlooker and shared to social media shows shoppers ducking for cover near an entrance in the aftermath.

The motive for the shooting is unclear but local journalist Jacob Beltran tweeted that witnesses heard arguing just moments before shots rang out.

"We don't know right now what the motive was. There's a couple of theories that we're looking at. But right now, we just don't know," Chief McManus said.

"Right now there's no further danger in the mall. People did run, understandably, but things are calm now.

"Crime scene investigators are processing the scene and detectives are canvassing for witnesses and further evidence."

A manhunt for the gunmen is now under way.

Julian Castro, running for the Democratic nomination for president, also a San Antonio native, expressed his shock.

"As we await more information, my heart goes out to the victims, their families, our city, and our country," Mr Castro tweeted. "Enough is enough — we must act on gun reform now."