Houston police said they were responding to reports of shots being fired on Tuesday at Ben Taub Hospital, a major healthcare center in the city.
There were no indications yet if anyone was injured or killed. Live aerial coverage provided by Houston TV station KHOU showed officers outside the facility, at one point with a few drawing their weapons, and patients on gurneys being wheeled out of the hospital.
Police said they dispatched a SWAT team to the scene. Hospital officials were not immediately available for comment.