SAVAR, Bangladesh — Police in Bangladesh took six people into custody in connection with the collapse of a shoddily constructed building that killed at least 348 people, as rescue workers said Saturday that voices of survivors are getting weaker after four days of being pinned under the increasingly unstable rubble.
Still, in a boost for the rescuers, 29 survivors were pulled out Saturday, said army spokesman Shahinul Islam.
Most of the victims were crushed by massive blocks of concrete and mortar falling on them when the eight-story structure came down on Wednesday morning — a time many of the garment factories in the building were packed with workers.
It was the worst tragedy to hit Bangladesh’s massive garment industry, and focused attention on the poor working conditions of the employees who toil for $38 a month to produce clothing for top international brands.
Among those arrested Saturday were two owners of a garment factory, who a Dhaka court ruled can be questioned by police for 12 days without charges being filed. Also detained were two government engineers and the wife of the building owner, who is on the run, in a bid to force him to surrender. Late Saturday, police arrested another factory owner.
Violent public protests continued sporadically in Dhaka and spread to the southeastern city of Chittagong where several vehicles were set on fire.
Working round the clock since Wednesday through heat and a thunderstorm, rescuers on Saturday finally reached the ground floor from the top of the mountainous rubble through 25 narrow holes they have drilled, said Brigadier General Ali Ahmed Khan, the head of the fire services.
‘‘We are still getting response from survivors though they are becoming weaker slowly,’’ he said, adding that rescue workers were now able to see cars that were parked at the ground level.
‘‘The building is very vulnerable. Any time the floors could collapse. We are performing an impossible task, but we are glad that we are able to rescue so many survivors.’’ He said the operations will continue overnight as chances fade of people surviving for a fifth day with possibly grievous injuries and the heat.
The building site was a hive of frenzied activity all day with soldiers, police, and medical workers in lab coats working nonstop. Rescuers passed bottles of water and small cylinders of oxygen up a ladder leaning against the side of the building to be given to possible survivors inside.
They used bare hands and shovels, passing chunks of brick and concrete down a human chain away from the collapsed structure.
Nearby, Abul Basar wept as he awaited news of his wife, who worked in one of the garment factories. ‘‘My son says that his mother will come back someday. She must return!” he cried.
The bodies were kept at a makeshift morgue at the nearby Adharchandra High School before being handed over to families. Many people milled around at the school, waving photos of their missing loved ones.
Jahangir Kabir Nanak, junior local government minister, put the death toll at 348. Military spokesman Shahinul Islam said 2,429 survivors were accounted for, including 29 who were pulled out Saturday.
Shamsul Haque Tuku, junior home minister, said police had arrested Bazlus Samad, managing director of New Wave Apparels Ltd., and Mahmudur Rahman Tapash, the company chairman. He told reporters that police had also detained the wife of Mohammed Sohel Rana, the owner of the collapsed Rana Plaza building, for questioning.
The top three floors of the eight-story building were illegally constructed. Military spokesman Shahinul Islam said officials arrested Aminul Islam, chairman of Phantom Apparels Ltd., late Saturday in Dhaka.
Authorities are still searching for Rana, a local politician, who hasn’t been seen publicly since the building collapsed. Negligence cases have been filed against him. Police in Bangladesh often detain relatives of missing suspects as a way to pressure them to surrender.
Habibur Rahman, Dhaka police superintendent, said Rana was a local leader of ruling Awami League’s youth front. His arrest, and that of the factory owners, was ordered by Prime Minister Sheikh Hasina, who is also the Awami League leader.
Police said they detained for questioning two engineers working for the Savar municipality, Imtemam Hossain and Alam Ali.
They did not say what role they played in approving the design of the building but it was clear that the arrests amounted to a widening crackdown.