Hope was fading on Friday for 44 construction workers buried for days in the rubble of a building that collapsed in South Africa.

Authorities say rescuers are now faced with the challenge of moving thousands of tons of concrete with heavy machinery to see if there are any more survivors.

The death toll rose to nine after a worker who was in a critical condition died in the hospital, authorities said.

Of the 28 workers rescued from the site, 21 were in critical condition or had life-threatening injuries following Monday’s collapse of the five-story apartment complex that was under construction.

With fears that the final death toll could exceed 50, authorities in the city of George on South Africa’s south coast said large earth-moving equipment had arrived and rescue teams were removing huge slabs of concrete and rubble to reach deeper into the wreckage.

City authorities said it was still a rescue rather than a recovery operation, but no survivors have been located or brought out since Wednesday.

“Despite the introduction of large machinery, rescue techniques will still be applied meticulously and sensitively by the highly skilled and experienced disaster management team,” the city said in a statement.

It also revised the number of missing from 38 to 44 after determining that there were more construction workers at the site than previously thought.

New information provided by the construction company showed there were 81 workers when the building came crashing down, not 75 as authorities had initially announced, it said.

More than 600 personnel are involved in the rescue operation, with many brought in from nearby towns and cities.

George, which is about 400km (250 miles) east of Cape Town, is a small city known as a holiday and golfing destination.

Authorities say multiple investigations are under way into the cause of the collapse, including by police, the provincial government and the national department of labor.