Atlanta, Georgia (CNN) -- Zoo Atlanta announced Monday that it closed its gorilla exhibit after a silverback gorilla charged a window separating the animals' habitat from a viewing area, cracking the window and leading zoo personnel to order zoogoers to flee.
The incident occurred about 2:15 p.m. Sunday as zookeepers at the Willie B. Conservation Center were tossing pieces of orange to the gorillas, who appeared to be munching happily on them in the 90-plus-degree heat.
All of a sudden, what appeared to be the largest of the animals, 20-year-old Taz, fixed his gaze on a point inside the viewing area. Among the people standing inside was a woman dressed in blue scrubs, with a stethoscope.
From about 15 yards away, Taz began walking and then running toward the window that separated the animals from about two dozen visitors, all the while keeping focused on a spot inside the viewers' area.
A few feet from a floor-to-ceiling glass window -- one of several that face the animals' habitat -- Taz hurled himself into the glass, landing with a thud and cracking it in various places.
At that, pandemonium erupted inside the viewing area as parents scooped up their children and stumbled over one another to hightail it toward the exit on the other side of the building.
Several employees who were inside the viewing area ordered all non-zoo personnel out and then parked a golf cart in front of the door, presumably to ensure that no animals reached the pedestrian area.
"Taz exhibited this behavior most likely because he had undergone a routine medical exam the previous day and was concerned about the presence of veterinarians in the viewing area," the zoo said in a news release.
"Gorillas often associate their veterinarians as the ones giving vaccinations and can react nervously -- much like many people do with a visit to the doctor or dentist," said Dr. Hayley Murphy, director of veterinary services, in a statement released by the zoo.
Immediately afterward, the gorillas -- including Taz -- were ushered into their overnight holding area, the statement said.
"World-class animal care and the safety of our guests and staff are of the utmost importance at Zoo Atlanta," said Zoo Atlanta President and CEO Raymond King. "We have many drills to prepare zoo staff for various incidents and that preparation allowed us to safely return Taz to his secure holding area with no injuries to either the public or to the animal."
"Neither guests nor staff was ever in any danger," the statement said.
The center will reopen once repairs have been completed, said Keisha Hines, a zoo spokeswoman. Asked whether the replacement pane would be thicker, she said, "We are going to take the appropriate time to explore all replacement options."
Such an incident is "very unusual," said Elizabeth Lonsdorf, director of the Lester Fisher Center for the Study and Conservation of Apes at the Lincoln Park Zoo in Chicago, Illinois.
"We've never had any incident remotely like that," she said of the Lincoln Park Zoo's current ape house, which opened in 2004.
Still, she added, "It's kind of standard gospel that you should not look a male silverback gorilla in the eye. ... Imagine yourself: You're in your house; a stranger walks up to your window and starts staring you down."