Dhaka, March 7 -- Many people have been trapped under the rubble of a building at Siddique Bazar after an explosion killed at least 17 people and injured over 100 others in the crowded marketplace in Old Dhaka.

"We have to cut through the concrete to rescue them. The fire service is working on it," Hafiz Akter, additional commissioner of Dhaka Metropolitan Police, said on Tuesday evening.

Eleven firefighting units were conducting rescue operations after the blast occurred around 4:50pm, according to the fire service control room.

Police officer Hafiz said there were "a lot of casualties". He described the explosion as the biggest in recent times.

This is the third blast in a week to claim lives following explosions at an oxygen plant ...