An eight-storey building on the outskirts of Dhaka containing several garment factories and thousands of workers collapsed on Wednesday, killing at least 82 people with many more feared dead.

Only the ground floor of the Rana Plaza in the town of Savar outside the Bangladesh capital remained intact when the block -- which one minister said was illegally constructed -- imploded at about 9:00 am (0300 GMT).

Armed with concrete cutters and cranes, hundreds of fire service and army rescue workers struggled to find survivors in the mountain of concrete and mangled steel which resembled the aftermath of an earthquake.

Corpses and the injured were evacuated from the higher reaches of the pile of flattened floors with makeshift slides made from cloth which just hours earlier was being cut into shirts and trousers for export to Western markets.

Hiralal Roy, a senior emergency ward doctor at the nearby Enam hospital where victims are being taken, told AFP that the death toll was 82 and at least 700 injured people had been treated at the hospital.

"The toll will rise as conditions of some injured were critical " he told AFP.

Some workers complained that the building had developed cracks on Tuesday evening, triggering an evacuation, but they had been forced back to the production lines by their managers.

"The managers forced us to rejoin and just one hour after we entered the factory the building collapsed with a huge noise," said a 24-year-old worker who gave her first name as Mousumi.

"I am injured. But I've not found my husband who was working on the fourth floor," she told AFP, estimating that 5,000 people worked inside the building, which also housed apartments, a bank and shops.

Home Minister Muhiuddin Khan told reporters that the building was illegal and violated the country's building code. The huge death toll was likely to raise further questions about safety in the garment industry.

Bangladesh has the second-biggest clothing industry in the world, supplying to major Western brands, but it is plagued by regular accidents and demonstrations from workers demanding better wages and working conditions.

In November, a fire at a garment factory on the outskirts of Dhaka killed 111 workers in the industry's worst accident.

One of the factories housed in the collapsed building in Savar was New Wave Style, which on its website lists Mango of Spain and Italian brand Benetton as among its top buyers.

Building collapses are common in Bangladesh as developers often flout the official construction code when erecting multi-storey structures.

More than 70 people were killed after a multi-storey garment factory collapsed in the Savar area in 2005.

In November at least 13 people were killed after an under-construction flyover fell down in the port city of Chittagong.