Dramatic CCTV footage showed a group of some 40 visiting students on a balcony section plunge as the floor gave way with a cascade of glass, metal and other material crashing onto the ground floor where several others were walking.
The collapse inside the Indonesian stock exchange building in Jakarta injured at least 75 people.
A Jakarta police spokesman said that it was an accident and not the result of an explosion.
"We are still investigating the cause, but for now our priorities are the casualties," Jakarta police spokesman Argo Yuwono told Metro TV.
There were no reports of any deaths. Mr Yuwono said those hurt had mostly sustained injuries to their legs and arms.
"The number of injured... from the floor collapse at the Indonesia Stock Exchange is 75," national police spokesman Setyo Wasisto told AFP.
A spokeswoman for Jakarta's Siloam Hospital said it had received 28 victims from the exchange.
About a dozen injured people were seen being carried from the building on stretchers, a Reuters witness said and police were cordoning off the two-tower, multi-storey building.
The Indonesian police's Traffic Management Centre tweeted that visitors and workers had been evacuated from the building in the aftermath.
Despite the chaos, stock exchange spokesman Rheza Andhika said trade continued as usual in the afternoon session.
The accident happened shortly after noon local time while the market was on its lunchtime break.
"There was a loud banging so people who inside immediately ran outside of the building," journalist Marlia Zein said.
Images circulated on social media showed a metal structure that had collapsed near a Starbucks cafe close to the entrance of the building.
The Indonesia Stock Exchange is located in the centre of Jakarta, and the local office of the World Bank is also housed on the 12th floor of the complex, according to its website.
- With Reuters and AFP
