"The fire broke out as we were cutting a beam to bring out what we believe was the last remaining survivor from the collapsed building. We managed to douse it, but as we came back we saw her dead," Ahmed Ali told AFP.
"She was a brave lady and fought until the end. We worked for 10-11 hours today just to try to bring her out alive. We took the challenge but we lost. It's broken all our hearts. Everyone became emotional," he said.
Fire fighters were seen weeping live on television after the death.
The female garment worker's battle for survival had touched the nation as people watched the rescue efforts on television.
The rescue teams had to postpone a decision to clean up the debris with cranes and earth-moving equipment just to make sure it did not harm her chance for survival.
A volunteer said although she was weak, she was able to make a feeble cry for help from underneath the debris on Sunday morning.
"When we first arrived on the scene, she pleaded with us to not to leave her. We gave her water, oxygen, saline and food. And she ate and hang on," said a volunteer involved in the rescue operation.
The eight-storey building that housed five garment factories caved in on Wednesday, killing at least 379 people and trapping thousands others, most female garment workers, Dhaka police officer Moshiuddowla Reza told AFP.
Some 2,500 people were rescued alive from the rubble, which included about 1,000 seriously injured workers many of whom had to have their limbs amputated to free them from the rubble.
Police earlier arrested the owner of the building and three proprietors of export-oriented garment factories for forcing the workers to work in the building despite it developing visible cracks a day before the tragedy.