(WN): A hospital in Houston was locked down for nearly two hours Tuesday after getting reports of shots fired, but no evidence of an actual shooting or gunman was found inside, officials said.

Houston Police Chief Art Acevedo told reporters all six floors of the Ben Taub Hospital, including the basement, were searched by SWAT teams before they were cleared. Police dogs trained to detect gunfire found no evidence, according to Acevedo.

"I can't say there was no shooting," 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." Acevedo said a SWAT will remain on every floor of the hospital as a precaution. The police chief said authorities received "multiple reports" of a white male of an unknown age described as the suspect around 1:58 p.m. local time.

Acevedo said "multiple people" reported hearing a man say "Drop the gun! Drop the gun!" Witnesses also reported hearing "two large bangs," the chief said. "It's a hospital," he said. "Who knows what the bangs were?" Authorities are checking security cameras, in addition to interviewing those that called 911, to figure out what exactly sparked the commotion.

Acevedo praised the response time of the law enforcement to the scene and quickly securing the area. "It's clear when you have active shooters, they wreak a lot of havoc and injure a lot of folks," he told reporters. Television images from helicopters showed dozens of employees leaving the hospital, some of them attending to patients who were evacuated on gurneys or in wheelchairs.

Ben Taub Hospital is one of the hospitals that's part of the Houston's Texas Medical Center and one of the major trauma centers in Houston. Houston police and the Harris County Sheriff's Office dealt with a previous shooting inside Ben Taub Hospital on the fifth floor on Oct. 5, 2016, when a deputy was forced to shoot a suspect, according to Fox 26.

The suspect in the previous shooting was in HCSO custody for a probation revocation hearing, and was brought to the hospital after complaining about seizures. After searching Ben Taub Hospital twice and interviewing witnesses about a reported shooting, the Houston Police Department gave an "all clear" Tuesday afternoon and returned control of the hospital back to medical staff. Although an early report indicated a shooter had been cornered on a floor of the hospital, Houston Police Chief Art Acevedo said that no evidence was found of an active shooter or shooting.

"It wasn't a mistake, there was a specific reason (we responded)," Acevedo said. "We had multiple witnesses that heard a man yell, 'Drop the gun, drop the gun.' Multiple people heard two large bangs, whether or not those were gunshots is subject to further investigation."

But Acevedo, who arrived on the scene shortly after SWAT officers arrived, said there was no evidence of a shooting, such as bullet casings, broken windows or bullet holes. Police did not find any victims during their first and second checks."All patients and employees are safe at this point," Acevedo said. Reports started coming in about 2 p.m. of shots fired, Houston police spokesman Kese Smith said.

Medical providers hid inside their offices at Ben Taub Hospital as Houston police responded to reports of shots fired inside the building. Others barricaded themselves in available areas of the hospital.

Patients in the Emergency Room told the Chronicle that hospital staff originally said the flurry of action was part of a drill but then began disconnecting patients from their IVs. Images showed nurses and others bringing patients outside on hospital beds and gurneys.

Around 2:00 p.m. Eva Arroyo was registering patients into the emergency room located on the first floor of Ben Taub, when she heard reports that there was an active shooter in the hospital. A code white was issued and Arroyo said she and other hospital employees immediately began sheltering in place. Nurses blocked off the doors with stretchers.

"We know we need to close the doors, windows and stay still, " Arroyo said. She said she positioned herself by two police officers who were monitoring a patient, who is also a prisoner. "If anything, there's two police officers out there, so I feel safe in a way, " She recalls thinking while inside.

Eventually a doctor told them it would be safer for them to evacuate outside of the hospital. As she anxiously stood outside Ben Taub, waiting to receive updates, she said sometimes she worries about someone walking into the hospital with a gun. "I mean who's going to see what they have under their jacket or in their briefcase?" She wondered. While she waited, hospital employees gathered a group of emergency room patients at picnic tables.

Other hospital employees checked their phones and looked onward at the hospital, waiting to receive word on if they could go back inside. Students at St. Marks Episcopal School in Bellaire were apparently in the hospital's cardiology unit not long before the reports of a shooting were made. Harris Health System posted on Twitter a photo and Tweet praising fifth grade students for donating artwork to the cardiology clinic.

The school would not answer a reporter's questions about whether the students were still at the hospital when the building was locked down. By about 3:45 p.m., at least three patients had been transferred by ambulance to other hospitals as other patients wandered around outside.

Baylor College of Medicine's security department issued an emergency notification of an "active shooter situation" about 2:15 p.m. The notification instructed college employees not to go to Ben Taub and ordered those already there to follow emergency response guidelines.

The last shooting at Ben Taub happened in October 2016, when an officer shot an inmate who had taken a medical student hostage. Ricky Hall, 46, was facing a parole violation and a host of new charges when he was shot by a sheriff's deputy after he took up an "edged weapon," according to Chronicle archives.

Days before his violent outburst, Hall who struggled with bipolar disorder and schizophrenia, his mother said was taken to the hospital for treatment of seizures.  Hall ultimately died from his wounds. More recently, a gun-wielding patient was shot by off-duty sheriff's deputies after he opened fire Jan.

3 inside the North Cypress Medical Center in northwest Harris County, sending receptionists diving under their desks. The 21-year-old gunman, whose name was not released, survived the incident after being shot multiple times, according to authorities.