An explosion which damaged a parking lot of a shopping mall in the Indonesian capital was caused by a large firecracker, police said.

"The explosion that took place was not caused by a bomb," Jakarta Police Chief Makbul Padmanegara said of the late Monday blast which injured seven people.

"Based on the investigation by the forensic laboratory and the bomb squad, the explosion was caused by a low explosive that we usually know as a firecracker," he told reporters at the scene Monday night. "A big firecracker" caused the blast, he said.

The device went off under an emergency staircase of the underground parking lot at the Graha Cijantung mall in East Jakarta around 7:30 pm. It damaged the wall near the staircase.

The mall is owned by the "Red Beret" foundation operated by the army's special forces unit Kopassus.

Padmanegara said a large-size firecracker had the capacity to damage a wall if it blew up next to it. The Jakarta police spokesman could not be immediately reached for comment on Tuesday.

One man suffered a serious hand injury in the blast while the others were only slightly hurt. A witness who was working on the floor above the blast said there was a strong scent of gunpowder.

The blast was the third in the city this year. On June 9 an explosion at the parking lot of a nightclub in centrel Jakarta injured five people. Two more bombs were found in front of two other nightspots that evening but were defused.