Reshma told her rescuers that she survived on dry food and water that had been tossed into the rubble in the first days after the collapse, BSS reported.
"I ate biscuits and water," she told rescuers. "But the stock dwindled two days ago."
She told doctors at the military hospital in Savar that she was wracked by thirst for the last two days of her saga, all of which was spent in the dark between floors that had pancaked in the collapse.
The rescued woman's mother-in-law, Ayesha, said she was overjoyed.
"I have not seen her yet, but I am very happy that she is alive," Ayesha said. "At least my grandchildren got their mother back. All my grandchildren are now overwhelmed."
The news spread widely and rapidly; within minutes, Prime Minister Sheikh Hasina phoned the unlikely survivor and asked about her condition, then flew by helicopter to visit her.
"It's an unprecedented incident," she said afterward, according to BSS.
The news agency said Reshma is from northern Bangladesh's Dinajpur district. She was working as a swing operator for Phantom Garment, which had a factory in the Rana Plaza when it collapsed on April 24.
In addition to the water sprayed over the mound early after the disaster, water may have trickled to the second floor from recent rains, or from fire hoses employed when firefighters extinguished the blaze that erupted during the failed rescue attempt.
The rescue, which came on the same day that officials raised the death toll from the collapse by 30 to 1,043, represented a ray of cheer against an otherwise grim tableau.
The building had held thousands of people, many of them garment workers.
Though rescue workers had pulled more than 2,400 others to safety, 10 days had elapsed since anyone had been found alive.
Since then, efforts have focused on retrieving corpses from the heap of broken concrete over which bulldozers and cranes have been used to speed the cleanup. But Hossain said use of the heavy equipment is limited to areas that recovery experts are certain hold no people.
Many of the bodies have been so decomposed that authorities have struggled to identify them.
"We are near the end," Islam said.
The owners of the building and the factories are under investigation over accusations they ordered workers to enter the building on the day of the collapse despite cracks that appeared in the structure the day before.
The Bangladeshi government has faced criticism for failing to tighten safety standards in the country's thousands of garment factories, where millions of people work.
The Savar building collapsed five months after a fire at a garment factory near Dhaka killed more than 100 people. And on Wednesday, eight people died in a fire at another factory in the area.
The European Union has threatened to take trade action against Bangladesh if it doesn't improve health and safety conditions for workers.
Western retailers and clothing brands that get their products from Bangladeshi factories are also under pressure to subject their supply chains to greater scrutiny.