Officials said Downey police confirmed there are no injuries and the building is being cleared.
Just before noon, the LASD Norwalk Station tweeted that they are assisting Downey police with a "fluid," emergency situation and "possible active shooter" at the hospital, located in at 9333 Imperial Highway.
Sheriff's officials confirmed shortly after that a suspect was detained for questioning. Meantime, officers and deputies searched the hospital "room by room, floor by floor."
Law enforcement is detaining 1 suspect. Numerous officers/deps are beginning to search/clear the building room by room, floor by floor. Unk if additional suspects or details of any victims. Please be patient and stay clear. For those in the #Kaiser building, shelter in place.— LASD Norwalk Station (@NorwalkLASD) September 11, 2018
AIR7 HD was over the scene as crowds of people evacuated the building with their arms up.
Several patrol vehicles blocked streets surrounding the medical facility as the investigation continued.