A military official, Maj. Gen. Chowdhury Hasan Suhrawardy, told reporters that search and rescue operations would continue until at least Saturday.
"We know a human being can survive for up to 72 hours in this situation. So our efforts will continue non-stop," he said.
Hundreds of rescuers, some crawling through the maze of rubble, spent a third day working amid the cries of the trapped and the wails of workers' relatives gathered outside the building, which housed numerous garment factories and a handful of other companies.
Police cordoned off the building site, pushing back thousands of bystanders and relatives, after rescue workers said the crowds were hampering their work.
Clashes later erupted between relatives of those still trapped and police officers, who used batons to disperse the mobs. Police said 50 people were injured in the clashes.
"We want to go inside the building and find our people now. They will die if we don't find them soon," said Shahinur Rahman, whose mother is missing.
Elsewhere, many thousands of workers from the hundreds of garment factories across the Savar industrial zone and other nearby industrial areas took to the streets to protest the collapse and poor safety standards.
Local news reports said protesters had smashed dozens of vehicles at one strike Friday. Most of the other protests were largely peaceful.
Dozens of people have been rescued from the wreckage well after Wednesday morning's collapse.
Forty people had been trapped on the fourth floor of the Rana Plaza building until rescuers reached them Thursday evening. Twelve were soon freed, and crews worked to get the others out safely, said Brig. Gen. Shikder. Crowds at the scene burst into applause as survivors were brought out.
Police say cracks in the building had led them to order an evacuation Tuesday, but the factories ignored the order and were operating when it collapsed Wednesday. Video shot before the collapse shows cracks in the walls, with apparent attempts at repair. It also shows columns missing chunks of concrete and police talking to building operators.