Rescue teams trying to find dozens of construction workers missing since a multi-story apartment complex collapsed in a coastal city in South Africa have made contact with 11 people buried alive beneath the mangled wreckage, authorities said Tuesday.

One man called his wife from underneath the rubble of the five-story building that had been under construction when it collapsed Monday, the head of the rescue operation said. That enabled emergency responders to locate the man, although he was still trapped and hadn’t yet been brought out.

Six workers have been confirmed dead and there are fears that the death count could rise sharply. There is no news on 37 other people unaccounted-for amid the huge slabs of concrete and metal scaffolding that came crashing down when the building collapsed in the city of George, about 400 kilometers (250 miles) east of Cape Town.