At least 87 people have been killed and many more are feared trapped after an eight-storey building collapsed on the outskirts of the Bangladeshi capital Dhaka, government officials say.
Firefighters and army personnel are leading the operation to rescue those caught beneath the debris in Savar.
More than 600 people have been injured. The death toll is expected to rise.
Building collapses are common in Bangladesh where many multi-storey blocks are built in violation of rules.
The Rana Plaza building contained several clothing factories, a bank and a market.
It collapsed at about 0900 local time (0300 GMT), during the morning rush hour.
Grieving relatives have been anxiously
waiting outside the collapsed building in
Savar. Rescue teams have been working
frantically using concrete cutters and
cranes digging through the rubble to pull
It is still not clear how many people are
trapped inside, although local media say
there are hundreds. A doctor at the local
hospital told the BBC that their services
had been stretched.
The reason for the collapse is not yet
known. The latest incident has once
again raised questions about safety
standards in the country's thriving
garments industry. However, factory
owners say safety standards have
improved significantly in recent years.
Sohel Rana, a local who rescued several people, told Bangladeshi newspaper The Daily Star that he had heard cries for help coming from under the rubble.
The scene looked like a "war zone", Dhaka resident Tahsin Mahmoo told the BBC, adding that appeals had been put out for citizens to donate blood.
Hundreds of people, anxious for news of friends and relatives, have gathered at the scene. Others are moving rubble using their bare hands.
"Already we've rescued three to four hundred people... Now we are cutting through the concrete walls and trying to get inside with the help of sniffer dogs," fire brigade chief Ali Ahmed Khan told the BBC Bengali service.
Police told local media that the rear of the building had suddenly started to collapse on Wednesday morning, and within a short time the whole structure - except the main pillar and parts of the front wall - had caved-in, triggering panic.
An eyewitness described the moment of the building's collapse: "It became completely dark on this side. There was a lot of dust from the collapsing debris, so we ran downstairs. When we came out we saw the whole building collapsed."
Only the ground floor of the building remained intact after the collapse, officials said.
It is not yet clear what caused the collapse, but local media reports said severe cracks were detected in the block on Tuesday.
One worker rescued from the building told the BBC that factory owners had told workers on Wednesday morning "not to worry" and that "they said they had examined the crack".
Speaking at the scene, Home Minister Muhiuddin Khan Alamgir said the building had violated construction codes and "the culprits would be punished".
Prime Minister Sheikh Hasina has announced a national day of mourning on Thursday in memory of the victims.
Bangladesh has one of the largest garment industries in the world, providing competitively priced clothes for major Western retailers which benefit from its widespread low-cost labour.
Tessel Pauli, a spokeswoman for the Amsterdam-based Clean Clothes Campaign, said activists at the scene had identified labels from European and US high-street brands.
"Immediate relief and long-term compensation must be provided by the brands who were sourcing from these factories, and responsibility taken for their lack of action to prevent this happening," she said in a statement to the BBC.
In November, a fire at a garment factory in a Dhaka suburb drew international attention to working conditions in Bangladesh's textile industry.
At least 110 people died, triggering a public outcry about safety standards.
Western retail chains that buy from factories in Bangladesh urged factory owners to improve safety standards.
The last major building collapse was in 2010, when a four-storey building in Dhaka caved in, killing at least 25 people and injuring several others.
In 2005, there was a building collapse near the site of Wednesday's incident, killing 64 people.