Orange County Global Medical Center in Santa Ana is on lockdown Tuesday morning after officials received a call of a man possibly armed with a gun in the hospital, police said.

Officers responded to the building, located in the 1000 block of North Tustin Avenue, after learning that the medical center had received an internal call regarding a man with a gun in the hospital, according to Santa Ana Police Department Cpl. Bertagna.

The call, which apparently involved some type of threat, came from a portable phone inside the hospital, said Jeff Corless, who is with the Global Medical Center. It was not exactly clear where the call was placed.

Authorities have also not indicated what time the incident started.

Police have been systematically combing each floor as they searched for the possible armed individual. However, as of 8:40 a.m., there was no evidence of a shooting or of an armed individual in the building, Bertagna said.

"We treat all these types of cases as … actual cases," Bertagna said. "Whether this is a hoax or not, we don't know."

The police activity was ongoing through at least 9:20 a.m., Sky5 aerial video showed.

Tustin Avenue has been shut down between 17th and First streets as authorities investigate the incident, police tweeted.