Hundreds of survivors of Bangladesh's worst industrial disaster blocked a main highway to demand wages Tuesday as the death toll from the collapse of a nine-storey building passed 700, officials said.

Around 3,000 garment workers were on shift at the Rana Plaza complex at the time of the collapse on the morning of April 24, making clothing for Western retailers such as Britain's Primark and the Spanish label Mango.

Many of the staff were earning only around 38 dollars a month, a salary condemned as "slave labour" by Pope Francis.

But with work having come to a complete halt, the employees are now demanding payment from factory owners, both for their wages and as compensation for injuries suffered when the complex caved in.

Police said around 400 survivors blocked a highway connecting the capital with the country's south and southwest on Tuesday by staging a sitdown protest.

The workers were chanting slogans, demanding "unpaid salaries and compensation", local police chief M. Asaduzzaman told AFP.

The protests came as the army revealed that dozens more bodies had been pulled from the rubble overnight.

Army spokesman Captain Shahid Ahsan Bhuiyan told AFP the number of bodies which had now been recovered stood at 705 and warned the toll could rise further as the recovery teams had only reached the fourth floor.

Authorities say 2,437 people were rescued alive from the ruins of the building, which housed a total of five garment factories.

Efforts to identify the victims are being hampered by the decomposition of bodies. Recovery workers, who are drawn from the ranks of the army and fire service, have to wear masks and use air freshener.

Fearful that Western brand names may turn their back on Bangladesh, the government announced a new high-level panel on Monday to inspect thousands of garment factories for building flaws.

The government made a similar announcement after a devastating fire swept a garment factory in November last year, killing 111 workers, but subsequent inspections were widely derided as insufficient.

A preliminary government probe has blamed vibrations from giant generators combined with the vibrations of sewing machines for the building's collapse.

Police have arrested 12 people including the complex's proprietor Sohel Rana and four garment factory owners for forcing people to work on the day of the accident, even though cracks appeared in the structure the previous day.

Factory workers have held protests calling for tough punishment for those responsible and stronger safety regulations.

Bangladesh is the world's second-largest garment exporter after China. The industry accounts for over 40 percent of its industrial workforce and 80 percent of the nation's exports.

Even before the latest disaster, the garment industry was struggling from the impact of a series of strikes as part of an ongoing battle between Islamist hardliners and police in the officially secular Muslim-majority nation.