There have been "multiple injuries and fatalities" in a shooting at an immigration facility in Texas, Department of Homeland Security Secretary Kristi Noem has said.

The attack happened on Wednesday morning at a Dallas field office for US Immigration and Customs Enforcement (ICE).

"Details are still emerging but we can confirm there were multiple injuries and fatalities," said Noem on X.

She added that the shooter had died of a self-inflicted gunshot wound. The incident follows a string of attacks on ICE facilities across the US in recent months.

"While we don't know motive yet, we know that our ICE law enforcement is facing unprecedented violence against them," Noem said. "It must stop."

Preliminary information suggests a sniper carried out the shooting from outside the facility and hit victims in a "secure detainee location", Acting ICE Director Todd Lyons told CNN.

He said three individuals were "down", including the suspected shooter.

"We're not sure on their condition," Lyons said.

Last month shots were fired at ICE offices in San Antonio, Texas, in what investigators described as a "targeted attack" against federal employees.

No injuries were reported in that incident, which ICE blamed on "political rhetoric" and "misinformation" about the Trump administration's detention policies.

Another shooting occurred on the 4 July public holiday at an ICE facility in Alvarado, Texas, after a protest escalated into a faceoff with police. An officer shot in the neck survived.