No one was found injured and there was no evidence that a shooting happened amid reports of gunfire Tuesday inside a hospital at the Texas Medical Center in Houston, authorities said.
"I can't say there was no shooting," Houston Police Chief Art Acevedo said. "I am confident if there was a threat, that threat is not present here now. We have thoroughly searched this facility on more than one occasion. There is no reason to fear."
He said dogs trained to detect gunfire found no evidence and that normal operations at Ben Taub Hospital, one of the city's major trauma centers, were resuming.
Officers were left on each floor as a precaution. The hospital has nearly 500 beds.
Witnesses reported hearing "two large bangs," the chief said.
"It's a hospital," he said. "Who knows what the bangs were?"
He said police received multiple reports of gunfire Tuesday afternoon, and dozens of officers and a SWAT team responded.
Hundreds of employees and some patients were evacuated. Patients on gurneys or in wheelchairs continued to be cared for outside the hospital. About two hours later, they were being returned inside.
Police searched all six floors and the basement of the hospital, then conducted a second search to make sure nothing was missed, Acevedo said.
Authorities also hope to examine surveillance videos as part of their investigation.
The hospital declared a "code white" emergency, an internal designation that set evacuations and other protocols in motion.
Video from NBC Houston affiliate KPRC showed dozens of employees leaving the hospital, some of them attending to patients who appeared to have been evacuated on gurneys or in wheelchairs.
Ben Taub is part of the Texas Medical Center, which bills itself the largest medical complex in the world.
It covers 1,345 acres a few miles south of downtown Houston, employs more than 100,000 people, includes more than 9,000 hospital beds and conducts more than 180,000 surgeries annually.