SAVAR, Bangladesh

Bangladesh Saturday made a series of arrests over the collapse of a factory complex which killed at least 341 as rescuers braved the stench of rotting corpses to detect further signs of life. Twenty-three people were pulled alive Saturday morning from the ruins of the eight-storey Rana Plaza compound which caved in at around 9:00am on Wednesday while thousands of garment workers were stitching clothes for Western brands.

But emergency workers warned their task was getting steadily harder as survivors were losing their strength to call for help. News of the arrests of two factory owners along with two engineers came after Prime Minister Sheikh Hasina vowed those responsible for the country's deadliest industrial disaster would be hunted down.

Bazlus Samad, the chairman of New Wave Buttons and New Wave Style factories, and Mahmudur Rahaman Tapash, a managing director, were detained shortly after midnight, Dhaka's deputy police chief Shyaml Mukherjee told AFP.

Police had filed a case against them for "death due to negligence", said Mukherjee. The overall owner of the building had still to be traced, he added.

The senior investigating officer Kaiser Matubbor told AFP that two municipal engineers who had given the building the all-clear after an inspection on Tuesday night had also been arrested and would face similar charges. Survivors have said the building developed visible cracks on Tuesday, but bosses ordered staff to return to the production lines.

Five factories were based in the complex at Savar, just outside Dhaka.

Hundreds of relatives of missing workers have massed at the site to witness the search for their loved ones.

Akram Hossain, a deputy director of the fire service, told AFP there were still some survivors trapped in pockets of the wreckage but warned their chances were "diminishing by the minute". Rescue workers, who include volunteers and soldiers, said survivors were becoming too weak to call out for help. "The stench of dead bodies is so strong that we have to work with one hand and air freshener in the other," Al Amin, a volunteer, told AFP. Naim, a fellow volunteer, spoke of the traumatic conditions facing rescuers.

"Inside the wreckage it's too smelly, hot and humid. I saw ashen colour decaying bodies with their intestines burst out," he told reporters.

Mahbubur Rahman, the fire service's director of operations, said rescuers were carving tunnels through the wreckage and bodies could be seen everywhere.

"There are some survivors. We can hear their feeble cries or them talking to each other," he told AFP.

"Pillars and beams are the biggest problem. Sometimes even if we can locate survivors, we can't reach them because of these beams. They take a lot of time to cut through."

Rescuers have so far only used hand tools like cutters and drills, fearing heavier equipment could dislodge masonry.

Although the discovery of more survivors gave fresh impetus to the rescue effort, there was growing anger at its pace.

"I've been here since Wednesday. We still don't know what happened to my aunt and sister-in-law," said Harunur Rashid.

"The rescue work is going on very slowly. There are too many people, yet too little work. Had they stepped up cutting of the concrete, I think they could save quite a lot of people," he said, clutching photos of his relatives.

Merina Begum, among those rescued on Saturday, said she and seven fellow workers trapped in the same area had been without food or water since Thursday.

"This morning when the rescue workers brought juice, ice cream and cold water, it was tastiest food I've ever had," she told AFP.

With many of Bangladesh's 4,500 factories shut due to protests, bosses declared Saturday a holiday and unions called a strike for Sunday.

Several thousand garment workers protested Saturday near the disaster site but they were dispersed by police firing rubber bullets and tear gas.

Bangladesh is the world's number two garment manufacturer and the industry is the mainstay of the economy. But it has a shocking safety record, with a factory fire killing 111 people in November.

Britain's Primark and Spain's Mango have acknowledged having their products made in the block, while other brands including Walmart are investigating.

The accident has prompted new accusations from activists that Western firms place profit before safety by sourcing their products from a country where textile workers often earn less than $40 a month.