Officials in the city of George, Western Cape province, say 26 people have been pulled from the wreckage and taken to hospital but there were dozens more workers were on the site when the building collapsed.

The cause is under investigation. Video footage taken nearby showed a huge cloud of dust as the building fell.

At the scene on Tuesday morning, emergency workers were taking it in turns to work 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 are still unaccounted for and it has been a long and slow process to bring survivors out.

Two of those pulled from the wreckage died of their injuries. Another three deaths were reported later by medics.

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 said shared his condolences to the families "and all those affected who continue to wait for word of their loved ones".

Heavy lifting equipment and sniffer dogs have been brought in to assist rescue efforts

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.

Officials said they had been able to establish contact with some of those under the rubble. There were thought to be at least 75 workers on the site when the collapse happened.

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 was quoted as saying by Reuters news agency.