At least nine people were killed and about 50 others injured in a blast at a garment factory in Bangladesh's Gazipur area, a police official said on Tuesday.The explosion took place on Monday night at Multifabs Ltd, an export oriented knitwear factory, reports Xinhua news agency.The blast at the factory's dyeing section led to a massive blaze that swept through the building for hours, he said."Eight bodies were recovered from the accident site," the official said, adding that one more person succumbed to his injuries later in a hospital.The death toll might increase as many people have sustained critical injuries, he said.Ataur Rahman, a Fire Service and Civil Defence Headquarters official, told the media that the ground and first floors of the four-storey building partially collapsed due to the blast.He said rescue operation was still under way. The cause of the accident is not yet clear.