A hospital in Sylmar was partially evacuated following a report of a man with a gun on Thursday, but no gunman was found after a floor-by-floor search and a massive response from authorities.

A nurse at the Olive View-UCLA Medical Center, located at 14445 Olive View Drive, reported seeing a man “brandishing a black handgun” on the second floor of the hospital about 9:20 a.m., the Los Angeles County Sheriff’s Department said in a news release.

“When he approached her she was not suspicious in any way until he produced a firearm which, in and of itself, produced a threat. She fled in fear for her safety and the safety of her patients,” said James Hellmold, chief of the sheriff’s Countywide Services Division. “It was in a threatening manner to her.”

Deputy personnel were notified of the sighting and the hospital was immediately placed on lockdown. Los Angeles police officers helped hospital staff and sheriff’s deputies evacuate the entire campus, the release stated.

Authorities responded to the medical center to search for the man, but the Sheriff’s Department stated in a tweet that it was not an active shooter situation. A SWAT team arrived at the hospital in an armored vehicle.

The team cleared the hospital floor by floor and searched outside as well. The campus was deemed safe, and normal operations at the seven-story hospital started up again about 12:30 p.m.

At least seven people were detained and then released during the search, officials said.

The nurse who reported the man described him as a Hispanic man in his 40s, “clean cut,” with medium length hair. He was last seen wearing a gray shirt and brandishing a black semi-automatic gun, Hellmold said during a press conference just before noon. He was further described at 5 feet 5 inches tall and 140 pounds.

Investigators are currently reviewing security footage to find an image of the reported gunman. The Sheriff’s Department said early Thursday evening that no surveillance video was “available.”

Shortly after the gunman was reported, aerial video from Sky5 showed dozens of people exiting the medical center as several patrol cars surrounded one of the entrances. About 200 inpatients and 700 outpatients, along with 500 to 700 staff members, were scheduled to be at the hospital Thursday, the hospital’s Chief Medical Officer Dr. Shannon Thyne said.

“The cops just told me, ‘You’ve got to back to your car and leave. There’s a shooter on the second floor,'” said Hugo Corona, an evacuee.

The medical center went into “internal disaster mode, which means we’re diverting all calls and all ambulance drivers to the facility,” hospital spokeswoman Lois Ramirez said.

Aerial video from Sky5 showed one patient being wheeled out of the building on a gurney and pushed down the street to another location. Areas with patients who could not be moved were asked to shelter in place, while those who could safely evacuate the medical center were asked to do so, said sheriff’s Lt. A.J. Rotella.

Thyne told KTLA that the staff did not transport any patients off the property and instead went into “diversion mode.”

“The patients who are outpatients, who are in ambulatory settings, along with the personnel in those areas, have all been evacuated,” Thyne said. “We did go on ‘diversion’ when this initially began and the ER stopped accepting ambulance transfers to our facility and those patients were redirected to other nearby hospitals.”

The Sheriff’s Department’s Countywide Services Division patrols county hospitals and thus handled the response even though Olive View is in the city of Los Angeles.

KTLA’s Melissa Pamer contributed to this article.