"There is no bomb element," he said.
Figures released by five hospitals showed 77 people were injured.
A spokeswoman for Jakarta's Siloam Hospital said it had received more than two dozen victims.
A college student from Palembang said she felt a tremor just before the floor collapsed.
"The structure suddenly collapsed, causing chaos," the student, identified as Ade, told MetroTV.
She said some of her friends were hit by debris and suffered head wounds and broken bones.
The stock exchange remained open for its afternoon trading session and its general manager, Tito Sulistio, asserted no one had been killed.
"I guarantee that there were no fatalities," he said. "I helped evacuate the victims to the park and as far as I know, the worst injuries are fractures."
He said the exchange will pay the students' medical costs.