Rescue workers were searching for survivors late into Wednesday night after a building containing five garment factories collapsed in Bangladesh, killing 124 people and injuring over 1,000.

Only the ground floor of the eight-storey Rana Plaza in Savar town just outside the capital Dhaka 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 in the hope of finding more survivors in the mountain of concrete and mangled steel, which resembled the aftermath of an earthquake.

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

"The whole building collapsed like a pancake within minutes. Most workers did not have any chance to escape," national fire department chief Ahmed Ali told AFP. "We can still hear the faint cries of some trapped people."

Fire fighters and soldiers cut through the building's collapsed floors and managed to rescue around hundreds of people, he said, adding "the search for survivors will continue through the night, for as long as it takes".

Hospitals in and around Savar were overwhelmed with patients with serious head and chest injuries and some without limbs, Hiralal Roy, an emergency doctor of Enam Medical College, said, adding the clinic treated more than 1,000 people.

"The death is now 124, most of them women," deputy police chief of Dhaka district A.B.M Masud Hossain, told AFP. Hossain is in charge of the unit responsible for identifying the bodies and retuuning them to their relatives.

The cries of people inside the rubble begging for rescue could be heard as thousands of relatives waited anxiously nearby, some chanting the name of Allah.

"Save us please!" a woman worker cried from inside. "We're 30 people here. Please save us."

Survivors complained that the building had developed cracks on Tuesday evening, triggering an evacuation, but they had been ordered back to the production lines.

"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.

Mustafizur Rahman, head of a police unit created to handle industrial troubles, said the factory owners, who have gone into hiding, ignored a warning not to open their plants.

"After looking at the cracks on Tuesday, we told them to keep the plants shut. They defied our call," he told AFP.

Factories in the building were making clothing for some top European retailers including Mango of Spain, according to campaign group Bangladesh Center for Workers Solidarity.

Mango spokeswoman Marta Soler Morera told AFP by email that it did not have any suppliers at the building, "although we did have contacts with one of them to produce a test production, as we do with several suppliers".

Tessel Pauli, a spokeswoman for the Amsterdam-based Clean Clothes Campaign, said the accident was "symptomatic" of problems in Bangladesh where foreign buyers often overlook safety problems in their hunt for higher profits.

According labour rights groups, it was the worst factory disaster in the country's history, prompting the government of Prime Minister Sheikh Hasina to declare a national day of mourning of Thursday when flags will fly half-mast.

The accident will likely pile more pressure on the Western bargain-hunters as the disaster came just months after a blaze in the Tazreen factory, which was making apparel for Walmart and others, left 111 people dead.

In the wake of that tragedy, the US threatened to cut some duty-free facilities for Bangladeshi products.

The Muslim-majority country has the second-biggest clothing industry in the world, but it is plagued by regular accidents and demonstrations by workers demanding better wages and working conditions.

Bangladesh Garment Manufacturers and Exporters Association said five factories were inside the building and together they employed around 3,000 workers.

Local media said the owner of the building was a local youth wing chief of the ruling party. He was rescued alive from the rubble.

Building collapses are relatively common in Bangladesh as developers often flout construction regulations when erecting multi-storey structures.

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