Rescuers are searching for survivors after an eight-storey building where clothing for Joe Fresh and other Western companies was manufactured collapsed near Bangladesh's capital, killing at least 161 people and trapping many more under a jumbled mess of concrete.

The death toll rose throughout the day, and army Brig.-Gen. Mohammed Siddiqul Alam Shikder said "many" people are still trapped. A clearer picture of the rescue operation would be available Thursday afternoon, he said.

Searchers cut holes in the concrete with drills or their bare hands, passing water and flashlights to those pinned inside the building near Bangladesh's capital of Dhaka.

"I gave them whistles, water, torchlights. I heard them cry. We can't leave them behind this way," said fire official Abul Khayer. Rescue operations illuminated by floodlights continued through the night.

Less than five months after a factory fire killed 112 people, the disaster again underscored the unsafe conditions in Bangladesh's massive garment industry. Workers said they hesitated to go to work Wednesday because the building had developed such severe cracks the previous day that it had been reported on local news channels.

Abdur Rahim, who worked on the fifth floor, said a factory manager assured them there was no problem, so they went inside.

"We started working. After about an hour or so the building collapsed suddenly," he said. He next remembered regaining consciousness outside the building.

Home Minister Muhiuddin Khan Alamgir told reporters during a visit to the site that the building had violated construction codes and "the culprits would be punished."

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More than 1,000 people were injured in the building collapse, according to Kalpona Akter, head of the Bangladesh Centre for Worker Solidarity (BCWS).

Akter said workers discovered a crack in the building on Tuesday but were asked to return work on Wednesday morning despite raising concerns over safety.

"These things keep happening because of the huge ignorance and negligence by the factory, by the government and, of course, by the Western tailors, who are sourcing their clothes from these factories," she told CBC Radio's As It Happens.

Clothing labels included Benetton, Joe Fresh

Among the businesses in the building were Phantom Apparels Ltd., New Wave Style Ltd., New Wave Bottoms Ltd. and New Wave Brothers Ltd., which make clothing for brands including Benetton, The Children's Place and Dress Barn. Workers said they didn't know what specific clothing brands were being produced in the building because labels are attached after the products are finished.

Joe Fresh, a Canadian company owned by Loblaw Companies Ltd., also issued a statement on Wednesday afternoon confirming that "a small number" of Joe Fresh-branded products were manufactured at the complex.

"We will be working with our vendor to understand how we may be able to assist them during this time," said the statement, which was attributed to vice-president of public relations Julija Hunter.

The statement also said Loblaw has "vendor standards" pertaining to how its products are made.

Sumi, a 25-year-old worker who goes by one name, said she was sewing jeans on the fifth floor with at least 400 others when the building fell.

"It collapsed all of a sudden," she said. "No shaking, no indication. It just collapsed on us."

She said she managed to reach a hole in the building through which rescuers pulled her out.

Reports suggested the death toll was likely to rise.

"We sent two people inside the building and we could rescue at least 20 people alive. They also told us that at least 100 to 150 people are injured and about 50 dead people are still trapped inside this floor," said Mohammad Humayun, a supervisor at one of the garment factories.

Tens of thousands of people gathered at the site, some of them weeping survivors, some searching for family members. Firefighters and soldiers using drilling machines and cranes worked with local volunteers in the search for survivors.

Teenager carried out

An enormous section of the concrete structure appeared to have splintered like twigs. Colourful sheets of fabric were tied to upper floors of the wreckage so those inside could climb or slide down and escape.

Bangladeshi Army personnel and civilian volunteers work on the scene at a building collapse in Savar, on the outskirts of Dhaka. (Munir Uz Zaman/AFP/Getty Images)

An arm jutted out of one section of rubble. The lifeless body of a woman covered in dust could be seen in another. A firefighter carried the body of what appeared to be a teenager from the area.

Rahim said his mother and father, who worked with him in the factory, were trapped inside.

"I have no idea what is going on," he said.

Mosammat Khurshida wailed as she looked for her husband. "He came to work in the morning. I can't find him," she said. "I don't know where he is. He does not pick up his phone."

The building, in the Dhaka suburb of Savar, also housed a bank and shops.

Industry powerful

At the morgue of the medical college, many wailed as they waited for the bodies of their loved ones. "Where's my mother? Where's my mother? Tell me, tell me, oh Allah, oh Allah," Rana Ahmed cried.

The November fire at the Tazreen garment factory drew international attention to working conditions in Bangladesh's $20 billion-a-year textile industry. The country has about 4,000 garment factories and exports clothes to leading Western retailers. The industry wields vast power in the South Asian nation.

Tazreen lacked emergency exits and its owner said only three floors of the eight-storey building were legally built. Surviving employees said gates had been locked and managers had told them to go back to work after the fire alarm went off.

Clothes with Disney, Wal-Mart and other Western labels were found at that factory.