Reports of shots fired at a Denver hospital Friday afternoon caused a massive police response as the Rose Medical Center campus was locked down for more than three hours, as surrounding streets were blocked off and emergency room traffic diverted.

Dozens of Denver Police Department SWAT members methodically swept the campus, zone by zone, looking for a gunman and victims. Neither was found.

“This is ongoing investigation,” said Tyrone Campbell, a police spokesman, at a 7:30 p.m. briefing. “We are not done.”

At 9:45 p.m. police said they had completed a search of the campus, “with no suspect or victims located.”

Police swarmed the medical facility after receiving multiple calls, starting at 4:17 p.m., of shots fired, Campbell said. The first officers on scene arrived within three minutes.

Officers with weapons drawn searched Rose Medical Center, while other officers cordoned off blocks around the hospital, at 4567 E. Ninth Ave., not letting people in or out.

The hospital placed patients and staff under a lockdown, which was lifted about three hours after police received the first calls about shots being fired. Police said there were no injuries and that reports of a gunman were unconfirmed.

Police said officers were looking for person of interest described as a white male in his mid-30s, weighing about 130 pounds and wearing a flannel shirt and a hat. Police stressed that there were no suspects.

“This is a very fluid situation. It’s an ongoing situation,” Campbell said. “We are open and ready for however this turns out.”

Patients and staff were told to shelter in place and stay away from windows, Rose Medical Center spokeswoman Julie Hogan said. At about 6:30 p.m., police lifted orders for those outside the hospital to shelter in place, but they kept roads near the hospital closed. At 8:15 p.m.,most surrounding roads remained closed.

ALERT UPDATE: #DPD looking for White male, mid 30's, 130#, wearing flannel shirt & hat in connection to #RoseMedCntr investigation. #Denver — Denver Police Dept. (@DenverPolice) September 16, 2016

At about 4:30 p.m., when the first reports were made of a possible gunman, the hospital was put under a “code silver,” which is the hospital’s code for an active shooter, said Deborah Polhill, a spokeswoman for Rose Medical.

Police and firefighters quickly swarmed the area. Melissa Taylor, spokeswoman for the Denver Fire Department, said firefighters were staging at the hospital per their standard response.

Dan Warvi, a spokesman for the Veterans Affairs Eastern Colorado Healthcare system including the VA Hospital next to Rose Medical Center, said their building was also placed on lockdown.

Warvi said there were no reports of any shooting at the VA buildings.

“University of Colorado Hospital is aware of the reported situation, and we are ready to care for patients if needed,” said spokesman Dan Weaver.

Denver Post staff reporters Kieran Nicholson and Kevin Simpson contributed to this report.