By Farid Ahmed, for CNN
DHAKA, Bangladesh (CNN) -- An eight-story building collapsed Wednesday morning on the outskirts of the Bangladeshi capital, killing at least 123 people and injuring hundreds, a police official said.
Broken concrete and twisted metal stuck out from the massive pile of rubble, where rescuers dug by hand to reach trapped workers. Dhaka District Police Chief Habibur Rahman said search efforts were continuing. It was unclear how many people were trapped in the ruins.
Video from the scene showed injured victims being whisked away on stretchers and crews carrying limp bodies from the rubble. Some onlookers wept while others frantically searched for missing loved ones.
Authorities said they did not know what caused the collapse of the building, where five garment manufacturers employing about 2,500 workers were based, according to the Bangladesh Garments Manufacturers and Exporters Association.
Several garment workers near the wreckage said a crack appeared Tuesday on the building's seventh floor.
At first, the workers said, managers ordered workers not to report to work on Wednesday.
Later, the factory owners reversed the order, telling workers that the building was safe, said Morjina Begum, who worked on the sixth floor. Many workers were hesitant to show up Wednesday but reported to work because they were afraid of losing their jobs, she said. More than a dozen other workers corroborated her story.
Managers for the garment manufacturers housed inside the building could not be immediately reached for comment.
Employees of the Savar branch of BRAC Bank were evacuated Tuesday after the crack was detected and were ordered not to show up on Wednesday, according to the national news agency, Bangladesh Sangbad Sangstha, citing a news statement from the bank.
None of the bank's workers was among the injured or dead, it said.
In addition, a general strike had shut a shopping mall on the two lowest floors.
Also on the second floor was a supplier to Primark, a UK retailer, the company said in a statement. "Primark has been engaged for several years with NGOs and other retailers to review the Bangladeshi industry's approach to factory standards," it said. "Primark will push for this review to also include building integrity."
The third floor was offices, garment manufacturers were on the fourth through seventh floors, and the top floor was a canteen.
Home Minister Mohiuddin Khan Alamgir said army troops, fire service personnel, police and Rapid Action Battalion troops had been mobilized to the site, about 25 kilometers (15.5 miles) from Dhaka.
"The fact is, we don't know yet how many people were killed actually ... but I can tell you the building was not built in compliance with the (safety) rules and regulations," Alamgir said.
"Stern legal actions will be taken against the people who built the structure defying the codes or laws."
Work was proceeding slowly in order to avoid causing a further collapse, said Maj. Gen. Abul Hassan Sarwardy, commander of the army's Savar-based 9th Division.
Six hundred people had been taken to hospitals in Savar and Dhaka and to a nearby military hospital, and 30 medical teams and other groups of doctors and paramedics were treating the injured at tents erected on the scene.
The commercial building housed three garment units, a branch of a bank and 300 shops, the national news agency reported.
Video showed two female garment workers pleading to be rescued. "Please retrieve us. ... Save my life," said a woman who identified herself as Sakhina.
A doctor at Enam Hospital said some victims had lost their hands, arms or legs.
A national day of mourning was set for Thursday.
The last major building collapse in the country occurred in 2005, when more than 70 people were killed in a garment factory collapse in the same area, the Bangladesh Sangbad Sangstha news service reported.
A fire at a clothing factory in a suburb of Dhaka in November killed at least 112 people.
Garments account for 80% of Bangladesh's $24 billion of exports.
The country has about 4,500 garment factories where workers make clothes for brands including Tesco, Walmart, JC Penney, Kohl's and Carrefour.
CNN's Samira Said and Sumnima Udas contributed to this report.