Visitors were left terrified when a glass ledge on the 103rd floor of the tallest skycraper in Chicago cracked under their feet.
The protective layer covering the glass splintered into thousands of pieces at the Sky Deck area of the Willis Tower, 1,353 feet above ground, on Monday night.
No one was injured, a spokesperson confirmed to CNN affiliate WBBM.
Video captured by one of the visitors, Jesus Pintado, shows visitors' horror as they stayed away from the sightseeing box.
He said: "There was a woman with two kids and they looked really pale and scared because the floor just cracked."
His wife Karly added: "I'm scared of heights in general, after I saw that happen, I was like 'nope, not going on'."
The glass sightseeing area extends out 4.3 feet from the 103rd floor and attracts about 1.5 million visitors each year.
The area, also known as the 'ledge', is designed to hold up to 4.53 tonnes and its protective coating is intended to keep the ledge from scratching.
Chicago’s Department of Buildings said the Willis Tower’s in-house engineers are handling the situation.
Local reports stated that a similar incident happened in May 2014 when the protective layer cracked.
Tourist Alejandro Garibay then told WGN he saw lines forming in the glass and immediately moved from the ledge.
There was no immediate danger in that incident.
