Updated at 10am

A mezzanine floor overlooking the main lobby of the Indonesia Stock Exchange building collapsed on Monday, injuring 77 people under a shower of glass and other debris, an exchange employee and witnesses said.

The building is part of a two-tower complex which was the target of a suicide bombing by Islamist militants in September 2000 but police ruled out a bomb as a cause of Monday's collapse.

Police cordoned off the complex as people fled the building, as the injured, including students visiting the building, were taken away by stretcher.

"We are focusing on the evacuation process right now," Jakarta police spokesman Argo Yuwono told Metro TV.

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.

The exchange resumed business in the afternoon. Its president said he believed the number of injured was below 20.

File photo: Reuters