Police in Oregon are looking for a suspect after a shooting at a hospital in downtown Portland left at least one person injured, authorities said.

Portland police said officers responded with a Crisis Response Team to Legacy Good Samaritan Medical Center in the northwest area of the city after reports of a person with a gun inside the facility, Sgt. Kevin Allen said in a news conference. The facility was placed on lockdown.

When officers responded, they were told a person had opened fire inside the hospital. At least one person was injured, Allen said.

"We were told that shots had been fired in the hospital," Allen said. A witness told officers the suspected shooter had already left the hospital by the time police arrived.

A Fred Meyer grocery store nearby was evacuated and searched by police, but Allen said authorities have not located the suspect.

"This is still considered an active tactical incident. There's efforts underway to locate the suspect," Allen said, adding authorities "no longer think there's any potential danger at the hospital."

Allen said officers from across the city were contributing to the search for the suspected shooter. The hospital will remain on lockdown as officers investigate, he said.

Jonathan Avery, the hospital's chief operating officer, called the shooting "an extremely scary situation."

"We really want to make sure that folks do not come to Good Samaritan today until everything has been cleared and we're back and open," Avery said.

Portland Mayor Ted Wheeler also advised residents to "stay alert" on Twitter.

"This is still an active investigation," the mayor wrote. "We urge those in the area to stay alert until further notice."