SAVAR, Bangladesh — Rescuers tunneling Friday into the rubble of the eight-story building that collapsed Wednesday discovered another 50 people trapped on what remained of its third floor, an official said.

Bangladesh Fire Service Deputy Director Maj. Mizamur Rahman said rescuers were hoping to free them within a few hours. As the effort was under way, they dropped food and bottled water to those who called out.

Also Friday, a woman who gave birth under the debris was rescued, along with her infant, a fire service official said, according to the state-run news agency Bangladesh Sangbad Sangstha (BSS). Earlier, the agency had reported two women had given birth; it did not explain the change.

The news of survival and new life came as the 72-hour deadline to change the operation from rescue to recovery approached, even as hundreds more people were feared still trapped amid the rubble.

Officials coordinating the operation have said the rescue efforts would end Saturday morning, when heavy equipment will be used to retrieve the remaining bodies and cart away the rubble.

“You can see heavy cranes and bulldozers here to quickly remove the concrete debris, but we can’t use them at the moment as our prime objective is to retrieve the people alive first,” the military spokesman said Friday.

The planned use of heavy equipment ignited protests from the people who crowded near the rescue site, many of them relatives who were showing pictures of the missing to whomever would pay attention and saying they did not believe 72 hours was long enough to wait.

Police used tear gas to disperse them, BSS reported.

At the rescue site, the death toll from the collapse rose Friday to 307 as thousands of Bangladeshis filled the streets of the capital city of Dhaka in anger and rescuers raced to find more survivors.

“Our prime target is to rescue the rest of the survivors alive, as we are running against time,” a military spokesman told reporters more than two days after the incident, BSS said. It did not identify the spokesman.

It was not clear how many of the products made in the factories in the suburban Dhaka town of Savar were destined for the U.S. market, but U.S. companies are major customers for Bangladeshi-made clothing.

In all, 2,375 people have been rescued, said Inter Service Public Relations Director Shaheenul Islam.

Seventy-two of them were recovered from the wreckage Friday, BSS reported, citing police.

Using hand drills and rod cutters, rescuers pierced the rubble of what had been the rear of the building and extracted 40 survivors, 20 of whom were then hospitalized in critical condition, BSS said.

The mound of concrete and steel, flecked with bolts of brightly colored cloth, had been an eight-story building housing five garment companies employing some 2,500 workers; a bank; a shopping mall; and offices.

Collapse came a day after cracks appeared

The collapse in suburban Dhaka occurred Wednesday morning, a day after cracks appeared in the structure. It has stirred outrage in Bangladesh over lax safety standards in the country’s key industry.

Most of the victims appear to have been garment factory workers, who had been told to report to work despite their concerns that the building’s structure was not sound. The cracks led the bank to order its employees not to report for work Wednesday, and the shops in the mall were closed because of a strike.

The Bangladesh Garment Manufacturers and Exporters Association announced Friday that all garment factories would be shut over the weekend “for treatment of victims of the Savar building collapse and completion of the rescue operation successfully.”

The association said it would pay the salaries and dues of workers of the stricken building by the first week of May.

Authorities have said they did not know what caused the collapse or how many people remained inside the debris. But a police official said relatives had reported 595 people still missing.

Demands for punishment

Prime Minister Sheikh Hasina on Friday ordered police to arrest the owners of the building and the factories so that they can “face legal actions,” her spokesman said.

“It is not an accident, it is a killing incident,” Information Minister Hasanul Haq Inu told reporters. “All, including owners and administrative officials concerned, must be put on the dock for the killing of people.”

The nation’s high court ordered Thursday that the owners, who are believed to be in hiding, appear in court Tuesday, CNN affiliate Boishakhi Television reported.

During protests Thursday, demonstrators carried black flags. Some set fires, and others used clubs to break the windshields of passing trucks.

Hundreds of workers lay siege to the head office of the Bangladesh Garment Manufacturers and Exporters Association at Karwan Bazar in Dhaka.

They demanded the arrest of the factory owners and called for the death penalty for Sohel Rana, the owner of the building.

The vice president of the garment association, Shahidullah Azim, said the organization had suspended the factories’ memberships.

The demonstrations in Dhaka continued Friday.

Questions for Western companies

The catastrophe is the latest to strike Bangladesh’s garment industry, which employs more than 4 million people — most of them women — and regularly comes under scrutiny for its slipshod safety standards.

It also raises questions for the Western brands that contract with factories here to make their products. According to BSS, the United States receives 23% of the products — more than any other individual nation.

Some of the blame must be shouldered by Western brands, said Matab Choudhury, director general of the British Bangladesh Chamber of Commerce, in an interview with CNN’s Max Foster.

“They go to Bangladesh, they ask for the buying agent and they say, ‘OK, we want 2 million of this garment. How cheap can you go?’ ” he said.

He accused some agents from Western companies of seeking out factories that are not in compliance with safety laws.

The U.S. State Department said Thursday it wasn’t able to provide details about whether American companies were connected to operations in the collapsed building.

But the disaster underscores “the urgent need for the government, owners, buyers, and labor to find ways of improving working conditions in Bangladesh,” said Patrick Ventrell, a State Department spokesman.

Bangladesh Housing and Public Works Secretary Khandaker Showkat Hossain told BSS that the government was planning to form a separate authority to monitor compliance with the country’s building code, which critics say is often flouted.

“We are seeking technical support from Japan’s government in this regard, as the Japanese are very sound in taking earthquake preparedness,” he said.

The last major building collapse in Bangladesh occurred in 2005, in the same area as Wednesday’s, and killed more than 70 people, the national news agency said.

A fire at the Tazreen Fashions Factory in another suburb of Dhaka in November killed at least 112 people. Tazreen had made goods for Walmart and Sears, though both companies said they were unaware that the factory had made goods for them.

— CNN’s Tom Watkins reported and wrote from Atlanta; journalist Farid Ahmed reported from Savar. CNN’s Jethro Mullen and Sumnima Udas contributed to this report.