A mezzanine floor at the Indonesia Stock Exchange in Jakarta collapsed, injuring scores of people – many of the visiting students – under slabs of concrete and glass.
Television footage showed a chaotic evacuation from the main lobby, which was strewn with debris, and people being helped out of the building.
Police said that at least 77 people had been injured under a shower of glass and other debris on Monday. The victims were described as having mostly suffered leg and arm injuries.
The building is part of a two-tower complex, which was the target of a suicide bombing by Islamist militants in September 2000. Police ruled out a bomb as a cause of the latest collapse.
Emergency services cordoned off the complex as people fled the building, while the injured – including students visiting the building – were taken away by stretcher.
Jakarta police spokesman Argo Yuwono said: "The accident happened at the first floor… It’s a floor where many employees are passing by… there are some victims, but they have been taken to a nearby hospital."
Images aired on television and circulated on social media showed a mangled metal structure that had collapsed around a Starbucks cafe near the entrance to the lobby.
"The second floor of the building has collapsed," said Vindy, a personal assistant to the exchange’s president director, Tito Sulistio, who was in the building at the time.
"Slabs of concrete started to fall, there was lots of dust. Water pipes had burst," said Megha Kapoor, who works in the building and was in the lobby at the time.
"I heard a loud cracking sound. I saw a lady unconscious stuck under slab of concrete," she said, adding that the collapsed level was just above the reception desk.
She said there had been group of high school students on the level when it started collapsing.
Mr Yuwono said hundreds of students were visiting the stock exchange at the time of the collapse.
MetroTV reported that 15 ambulances were sent to the scene to take victims to hospitals.
A spokeswoman for Jakarta’s Siloam Hospital said it had received more than two dozen victims.
Despite the chaos, stock exchange spokesman Rheza Andhika said trade continued as usual in the afternoon session.
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The accident happened shortly after noon local time (5am GMT) while the market was on its lunchtime break.
"There was a lound banging so people who were inside immediately ran outside of the building," said Metro TV journalist Marlia Zein who was on the scene.