Efforts are continuing in South Africa to find about 50 people who went missing after a five-story apartment building collapsed on Monday.

At least six people have been confirmed dead since the incident in the southern coastal city of George.

Rescuers heard from 11 more survivors in the ruins of the under-construction building on Tuesday.

They include four who are trapped in the basement. The cause of the collapse is being investigated.

At the scene on Tuesday, emergency workers were taking it in turns to work on the small site, removing concrete blocks and debris by hand.

Every so often, the team leader raised his fist, calling for silence. Everyone stopped and looked on in the hope that someone had been found. Some of them were false alarms and the noise resumed.

The majority of the workers who were on the construction site – thought to be at least 75 in total – are still unaccounted for and it has been a long and slow process to bring survivors out.

“They will then begin a process of lifting the different floors off each other,” said Colin Deiner, chief director for disaster management.

“There is a possibility people could still be alive,” he added.

The entire rescue operation is expected to take between four and five days.

Video footage taken nearby showed a huge cloud of dust as the building fell.

The site has been cordoned off from the public. But there were still many people standing around the perimeter in shock and disbelief.

South African President Cyril Ramaphosa said his thoughts were with the families of people who died in the incident and called for the investigation to “bring closure to the community and prevent a repeat of this disaster”.

The city’s mayor, Ald Van Wyk, sent his condolences to the families “and all those affected who continue to wait for word of their loved ones”.

Overnight, more than 100 rescuers with sniffer dogs worked to locate those trapped in the building. Heavy lifting equipment was used to assist the operation.

Photos of the area now show a completely flattened construction site, with parts of the building’s roof lying atop the rubble.

“I saw one guy was working and then ‘boom’ and I saw the whole building collapsed… I’m also traumatised. It is very sad,” local councillor Theresa Jeyi said.