Savar, Bangladesh (CNN) -- Bangladeshi authorities arrested four people, including two factory owners, after at least 340 people died in a building collapse near the capital this week. Many others were trapped under concrete rubble; nearly 600 remain missing.
The owner of the building itself remains at large. Sohel Rana, has gone into hiding, said police, who are questioning four of his relatives, including his wife, in a bid to find him.
Police identified the arrested garment factory owners as Mahmudur Rahman Tapash and Bazlul Samad Adnan. Two government engineers also were arrested, police said.
Night fell in the capital Saturday, and rescue efforts continued for the fourth day -- beyond the 72-hour deadline since the collapse when authorities had said they'd switch from rescue to recovery mode, a decision that solicited vehement protests from those saying it was premature.
Even after that milestone had passed, supplies of fresh oxygen, food and water helped keep alive some who had been located but who were still trapped, the state-run BSS news agency reported.
"We will proceed with our campaign to rescue the last of the survivors alive," said Maj. Gen. Hassan Sarwardy, who is leading the effort.
Authorities have said they will decide on Sunday morning whether to shift the operation from a rescue mission to a recovery mission.
Crowds of relatives of the workers who were in the building pleaded for the intensification of rescue efforts that they say have slowed as the days have passed.
"There were hundreds of workers, now we're not getting them back, alive or dead," one woman said. "Please let us get to them, either dead or alive."
Prime Minister Sheikh Hasina on Friday had ordered police to arrest the owners of the building and the garment factories in it 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."
Most of the victims appear to have been garment factory workers.
Amid the arrests, the death toll mounted as families of the missing hoped for a miracle.
Rescuers pulled out a woman who had given birth in the mangled mess of the crumbled eight-story building, the state-run news agency Sangbad Sangstha reported. It was unclear Saturday how the mother and the baby were doing a day after they were rescued.
But most reports coming from the fallen structure near the capital, Dhaka, were of woe.
Officials originally planned to end the rescue efforts Saturday morning and bring in heavy equipment to retrieve the remaining bodies, but pushed that decision back for another day.
At a nearby medical college hospital, "thousands of survivors have been treated," said Sajjad Hussein, a spokesman for an anti-corruption agency.
"The crisis for blood is acute and the hospital authority is urging people to donate blood for the victims. There is also a shortage of medicine. The local military hospital is also treating patients."
Looking for loved ones
The picture of despair was clear Friday at a nearby local school, where bodies were being kept. Hundreds amassed, many of them relatives desperately searching for loved ones.
"People with photos of their relatives, mostly workers of the apparel factories, are asking the officials there for help. Whenever an ambulance is arriving at the spot, everyone is rushing towards (it) hoping to find at least the body of their near and dear ones," Hussein said.
In all, more than 2,400 people had been rescued, police said.
But it may take some time until the full extent of the destruction will be known.
The collapse 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.
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. But garment factory workers were told to report to work despite their concerns that the building's structure was not sound
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."
CNN's Lateef Mungin reported from Atlanta; journalist Farid Ahmed reported from Savar. CNN's Jethro Mullen, Greg Botelho and Sumnima Udas contributed to this report.