A mezzanine floor overlooking the main lobby of the Indonesian Stock Exchange building collapsed on Monday, injuring scores of people, officials and witnesses said.
The high-rise building, constructed in the late 1990s, is part of a two-tower complex also housing offices of the World Bank and the International Finance Corporation.
A Jakarta police spokesman said the collapse was an accident and not the result of an explosion.
The officials and witnesses said at least 77 people had been injured.
No deaths had been reported, said Triana Tambunan, business development manager at MRCC Siloam hospital, one of the hospitals near the stock exchange.
"Up to now we've registered 30 people," Tambunan told reporters.
"The bone fractures may be serious. We need to carry out further evaluations," she said, adding there were at least three suspected fractures.
Police cordoned off the complex as people fled the building, and the injured, including visiting university students, were taken away by stretcher.
Stock exchange president director Tito Sulistio said their treatment would be paid for by the exchange.
Images aired on television and circulated on social media showed a concrete and metal structure that had collapsed around a Starbucks coffee outlet near the entrance to the lobby of the building with blue-tinted windows.
Safety standards are often loosely enforced in Indonesia.