(CNN) -- A gunman and another person were killed during a shooting Tuesday at a medical building near the Renown Regional Medical Center, said Tom Robinson of the Reno, Nevada, Police Department.
Two other people were wounded and were in critical condition, Robinson said.
The shooter died of a self-inflicted gunshot wound, authorities said. Police don't have a motive, but Robinson said it was not a random act.
Kat Raco, an ophthalmic technician who works on the second floor of the Nevada Advanced Medicine building, told CNN that she heard at least two large booms and then the sound of scampering feet above her.
The shooter opened fire after going to the urology office of Nevada Advanced Medicine on the third floor, said Sharon Spangler, spokeswoman for Reno Police.
Raco said she and others in her office were seeing patients when the shooting occurred and first thought someone or something had fallen.
Police were there quickly, she said, telling them to lock the doors and not let anyone in.
About 10 minutes after that, more police escorted everyone on the second floor to a catwalk between the building and a parking garage. A plain-clothed officer asked questions before staff was allowed to leave about 45 minutes after the shooting.
"The police handled it in the best way possible," Raco said. "They were very professional and calm. Everyone (in the office) stayed pretty calm."
Raco said there are no armed guards in the building.
Reno police said there were at least two dozen witnesses to interview.
Earlier, the University of Nevada police tweeted that there was an active shooter and faculty, staff and students should find shelter where they were.
CNN first learned of the shooting through the university police department's Twitter account.
The medical center describes itself as the only Level II trauma center in that region of Nevada and is home to the area's only Children's Hospital, its website says. The facility also offers the region's largest number of clinical research trials.
Last month, there was a hospital shooting in Wisconsin when police shot and wounded an armed man on the neonatal intensive care floor of a Milwaukee-area children's hospital, authorities said.
Milwaukee police had gone to the Children's Hospital of Wisconsin to arrest the man on a felony warrant and found him holding a child in the intensive care unit, authorities said. Instead of surrendering, the man took out a handgun and fled down a hallway, prompting police to shoot him.
CNN's Chandler Friedman and Steve Almasy contributed to this report.