A mezzanine floor overlooking the main lobby of the Indonesian Stock Exchange building collapsed Monday, injuring scores of people, many of them students, under slabs of concrete and other debris, 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 Corp. It was the target of a car bombing by Islamist militants in September 2000.

Police ruled out a bomb as a cause of Monday's collapse. They said at least 77 people had been injured.