Bangladesh rescuers say that more than 500 people had likely died in a garment factory block that collapsed last week as the Pope condemned the use of "slave labour" in the local clothing industry.
As bulldozers and cranes worked to remove the rubble of the eight-storey building on the outskirts of Dhaka, senior army officers said the number of confirmed dead now stood at 405 but 149 people were still missing.
The country's worst industrial accident, which has focused attention on the use of factories in Bangladesh by Western clothing companies, drew tens of thousands of protesters onto the streets of the capital.
Workers holding red banners and flags chanted "Hang the killers, Hang the Factory Owners!" during a May Day rally that was largely peaceful unlike larger and more angry protests held since last Wednesday's disaster.
At the Vatican in a private mass for followers, Pope Francis weighed into the controversy, speaking out against labour conditions in Bangladesh, which are regularly decried by campaigners.
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"A headline that really struck me on the day of the tragedy in Bangladesh was 'Living on 38 euros a month'.
That is what the people who died were being paid. This is called slave labour," the Pope was quoted by Vatican Radio as saying. In fact, wages are even lower, with the legal minimum salary routinely paid to employees only $US38 ($A37) a month for a six-day week with 10-hour shifts.
The Bangladesh government faces growing foreign pressure to take credible moves to improve conditions in the garment industry, with the collapse at the Rana Plaza factory complex only the latest in a series of deadly disasters.
A fire at a textile factory last November left 111 people dead, and there have been widespread accusations that safety standards are both too lax and rarely enforced in the $US20-billion ($A19-billion) sector.
The European Union said late on Tuesday that it would look at steps to promote better practices after a host of European retailers including Primark, Benetton and Mango admitted using factories in the collapsed building.
Nearly 60 per cent of Bangladesh's garments are shipped to European Union free of duties and tariffs, giving the 27-nation bloc huge say over the country's workplace safety issues.
Anger in Bangladesh remains palpable and the demonstrations on Wednesday again saw demands for the building owner and four arrested factory bosses to face capital punishment.
They have been charged with death due to negligence. Many of the country's 4500 garment factories have been closed since last Wednesday, a major blow for the Bangladeshi economy which depends on garments for 80 per cent of its exports.
"We want the severest punishment possible for those responsible for this tragedy," said Kamrul Anam, head of the Bangladesh Textile and Garments Workers League.
"Enough is enough," said Liakot Khan, another of those taking part in the Dhaka protest, which echoed to the sound of drums and horns.
"The government should hang the building proprietor and the factory owners. We want justice for these murders."
Police put the number of protesters at the main rally in Dhaka at more than 20,000, and there were smaller-scale protests elsewhere in the capital and in other cities.
