Rescue teams worked through the night searching for dozens of construction workers buried for more than 12 hours under the rubble of concrete after a multi-story apartment complex that was being built collapsed in a coastal city in South Africa.

Authorities said early Tuesday that the death toll had risen to five, while 49 workers remained buried in the mangled wreckage of the building, which collapsed on Monday afternoon. Authorities said a further 21 workers had been rescued from the rubble and taken to various hospitals, with at least 11 of them suffering severe injuries.

The collapse happened in the city of George, about 250 miles east of Cape Town on South Africa's south coast.

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More than 100 emergency personnel and other responders were on the scene, using sniffer dogs to try to locate workers, some of whom were trapped under huge slabs of concrete that fell on them when the five-story building came down.

Large cranes and other heavy lifting equipment were brought to the site to help with the rescue effort and tall spotlights were erected to allow search and rescue personnel to work through the night.

Rescuers made contact with 11 workers trapped in the rubble and were hopeful of bringing them out, said Colin Deiner, the chief director of the provincial Western Cape Disaster Management and Fire and Rescue Services. He said some of them were talking to rescuers but couldn't move because they had limbs trapped under concrete.

"It's a very tough operation," said Deiner, who was at the scene. "There's a lot of concrete ... so we think it will still take quite a while. The search operation will continue all day. We've got a lot of people on the scene but it's really, really hard work."

"So many people trapped in a building like that is like searching for a needle in a haystack. You literally have to break through the concrete and cut through the reinforcing."

There were 75 workers on the construction site when the building collapsed, the George municipality said. It said three teams of rescuers were working at separate sites around the collapsed building where they believed construction workers were likely to be.

Family and friends of the workers gathered at the nearby municipal offices.

"Our thoughts are with the families and all those affected who continue to wait on word of their loved ones," George Executive Mayor Leon Van Wyk said.

Authorities were investigating what caused the tragedy and a case was opened by police, but there was no immediate information on why the building suddenly collapsed. CCTV footage from a nearby home showed the concrete structure and metal scaffolding around it come crashing down at 2.09 p.m. on Monday afternoon, causing a plume of dust to rise over the neighborhood.

People came streaming out of other buildings after the collapse, with some of them screaming and shouting.

Marco Ferreira, a local representative of the Gift of the Givers nongovernmental organization, was at the site with a team to offer support and food and drink to the rescuers on Monday. Gift of the Givers is a charity that often helps during disasters in South Africa. It also provided three sniffer dogs and handlers to help with the search, Ferreira said.

"The situation at this stage is still very much in the rescue stages," Ferreira told the eNCA TV news channel. "We don’t know, it’s probably going to carry on for days. There are some cranes there to help lift some concrete. But it’s not a pretty sight."

The provincial Western Cape government sent Deiner, the head of its disaster response unit, from Cape Town to George to oversee the rescue operation and Western Cape Premier Alan Winde, the head of the provincial government, was also at the scene.

Winde said the provincial government had also sent extra resources to assist.

"All the necessary support has been offered to emergency personnel to expedite their response. At the moment, officials are focused on saving lives. This is our top priority at this stage," Winde said in a statement.

The national government was being briefed on the rescue operation, Winde said.