The BBC's Anbarasan Ethirajan at the scene says it is a race against time before officials bring in heavy machinery.
He says the smell of decomposing bodies is making some rescuers ill.
More than 350 people have died since Wednesday's disaster and hundreds more are missing.
On Sunday, two more people were pulled alive from the rubble of the eight-storey building in the suburb of Savar as the rescue operation entered its fifth day.
A group of about nine survivors was also located and teams were using light cutting equipment to try to reach them, our correspondent says.
Water and food are being dropped through gaps in the rubble, he adds.
But with hopes fading for those still trapped, officials plan to bring in cranes within the next few hours.
The army officer co-ordinating the rescue, Maj Gen Chowdhury Hasan Suhrawardy, said they would try to save the nine people first by using light equipment.
"But if we fail we will start our next phase within hours," he said.
This would involve heavy equipment including hydraulic cranes and cutters to bore a hole from the top of the collapsed building, he told reporters.
He said they still aimed to recover survivors as well as bodies.
"In this stage, we have no other choice but to use some heavy equipment," he said.
"We will start it within a few hours. Manual operation and use of small equipment is not enough."
On Saturday a total of 29 people were rescued from the destroyed Rana Plaza in the commercial suburb of Savar.
Police have so far arrested three garment factory owners and two engineers in connection with the disaster.
Factory bosses Mahbubur Rahman Tapas and Balzul Samad Adnan surrendered to police early on Saturday while Aminul Islam was arrested later the same day.
Police said they had ordered an evacuation of the building on Tuesday after cracks appeared, but that the factories ignored them and were operating the next day.
The municipal engineers are reported to have approved the safety of the building a day before it collapsed.
The owner of Rana Plaza, Mohammed Sohel Rana, has gone into hiding although police are questioning his wife.
Airport and border authorities have been alerted to stop him from leaving the country, reports say.
One minister has alleged that Rana Plaza was built without permits.
Thousands of relatives of missing workers are waiting at the site as survivors and the dead are pulled from the rubble.
Police said 353 bodies had so far been found, 301 of which had been identified. A further 2,431 people are known to have survived.
There is no official figure on the number of people still missing, but Akram Hossain, a deputy director of the fire service, said their chances of survival were "diminishing by the minute".
The fire service's head of operations, Mahbubur Rahman, said the rescue effort was becoming increasingly difficult for emergency workers as survivors were losing their strength to call for help.
"There are many dead bodies but our top priority is finding those who may still be alive," he told AFP news agency. "There are some survivors. We can hear their feeble cries or hear them talking to each other."
Mr Rahman said rescuers were digging tunnels through the rubble with bare hands, drills and shovels because they feared heavier equipment could cause further collapse.
"Pillars and beams are the biggest problem. Sometimes, even if we can locate survivors, we can't reach them because of these beams. They take a lot of time to cut through."
One of those who was rescued on Saturday, Merina Begum, said she and seven other workers had survived without food or water. She told AFP: "When the rescuers brought juice, ice cream and cold water, it was the tastiest food I've ever had."
Anger at the building collapse has triggered days of violent protests in Dhaka, although streets were said to be quiet on Sunday.
Bangladesh has one of the largest garment industries in the world, providing cheap clothing for major Western retailers that benefit from its widespread low-cost labour.
But the industry has been widely criticised for its low pay and limited rights given to workers and for the often dangerous working conditions in garment factories.
Rescuers are frantically trying to save about nine people located in the wreckage of a collapsed factory complex in the Bangladeshi capital Dhaka.