An apparent attack at the gate of a military base in Corpus Christi, Texas, on Thursday is being investigated as a terrorist incident, officials said, warning that while the gunman was dead at the scene, a second person may be tied to the violence.

Officials say shots were fired shortly after 6 a.m. at the north gate of Naval Air Station Corpus Christi. One sailor, a security officer, was injured but is expected to survive, officials said.

The gunman, who was not immediately identified, was dead at the scene.

FBI agent Leah Greeves called the incident "terrorism-related," adding "we may have a potential second related person of interest at large in the community, but we would encourage the public to remain calm, and if you see something say something."

Greeves said investigators from multiple agencies are "working like crazy" to understand exactly what happened, and said the effort and cooperation among investigators was "awesome to see."

She said the investigation was still "fluid" and declined to provide more information while the FBI continued to gather evidence. Navy officials referred additional questions about the incident to the FBI.

The shooting comes less than a week after officials in Washington announced that an attack last year at a naval air station in Pensacola, Florida, had been carried out by a Saudi Royal Air Force trainee who had been in contact with al-Qaida suspects. That attack killed three service members and injured eight others, and the gunman was killed by law enforcement officers.

That attack led to an overhaul of how U.S. military officials screen foreign military officers who come to the United States for training. An examination of the Pensacola gunman's phones by the FBI found he had been in contact with suspected terrorists since 2015, before he entered the United States.

Like Pensacola, the base in Corpus Christi includes training programs for foreign military students.