DHAKA (REUTERS) - Rescuers in Bangladesh searched through the wreckage of a factory on Friday, a day after it collapsed killing at least seven people and far fewer people were believed to have been trapped than an initial estimate of 100.

Soldiers and sailors in the port town of Mongla helped emergency services search through rubble and pull out nearly 50 survivors as well as two more bodies overnight. "Most of the people inside the building have been rescued alive but rescue operations are still going on until the last body is recovered," senior district official Mohammad Shah Alam Sardar said by telephone from the scene.

Soon after the accident on Thursday, police estimated that 100 people were trapped but the number was much lower, Sardar said. "We suspect only a few more bodies will be found under the debris." Thirty people were injured, officials said.

The factory, run by a subsidiary of the Bangladesh army, was still under construction in the town, 335 km (210 miles) southwest of the capital, Dhaka, when its roof collapsed.

The cause was still being investigated but one survivor told media the building's roof had come down first, adding that there might have been problems in setting up scaffolding.

Bangladesh has a poor record for building safety.

A complex of shops and small factories collapsed in 2013 killing more than 1,130 people, most of them garment workers.

The collapse of Rana Plaza, built on swampy ground outside the capital, Dhaka, ranked among the world's worst industrial accidents and prompted a global outcry for improved safety in the world's second-largest exporter of ready-made garments.