A gunman shot and killed eight people, including children, at a shopping mall north of Dallas on Saturday.

Hundreds of people were evacuated from the Allen Premium Outlets mall as eyewitnesses described a man firing indiscriminately at passers-by.

A police officer on an unrelated call killed the gunman after hearing shots. Police have yet to identify him.

President Joe Biden on Sunday called once again for Congress to tighten gun controls in the wake of the tragedy.

He said the attacker, using an AR-15 style assault weapon, gunned down innocents in "the latest act of gun violence to devastate our nation".

"Such an attack is too shocking to be so familiar," he added, calling on Congress to ban assault weapons and high-capacity magazines, and require universal background checks.

As of Sunday morning local team, at least three surviving victims were in critical condition, police said.

Allen Fire Chief Jonathan Boyd said seven people - including the gunman - were pronounced dead at the scene and two died later in hospital.

The victims' ages range from 5 to 51, according to a hospital spokesperson.

A police officer at the mall "heard gunshots, went to the gunshots, engaged the suspect and neutralised the suspect," Allen Police Chief Brian Harvey said.

Some witnesses described the gunman as dressed all in black and wearing combat gear. Footage taken after the gunman's death appeared to show an AR-15 style rifle lying near his body.

Texas Governor Greg Abbott described the shooting as an "unspeakable tragedy" and said the state was ready to offer any assistance to local authorities.