CAPE TOWN, May 10 (Xinhua) -- The death toll in the building collapse in South Africa rose to 12 on Friday, as the incident site was declared a "no-fly zone."

The multi-story building collapsed on Monday afternoon in the coastal city of George, located about 400 kilometers east of Cape Town in the Western Cape province. The reasons for the collapse, which included an underground parking garage, are still under investigation.

As the rescue operation surpassed 96 hours on Friday afternoon, 40 of the 81 trapped workers -- initially reported as 75 -- have been recovered from the collapsed building, said the municipal government of George in its latest update.

Twelve of the 40 retrieved workers have been declared deceased, while 41 are still unaccounted for, according to the update.

Meanwhile, the Airports Company South Africa has declared the incident site a no-fly zone, said the municipality. The decision followed reports of a private drone flying over the rescue zone on Thursday.

The airspace was cleared to allow only the rescue drones in the sky. "This restriction will be strictly enforced, and any individuals found violating it will be subject to criminal prosecution," it added.

In a separate statement issued by the Western Cape government, the head of the Provincial Disaster Management Center, Colin Deiner, said that the operation remains in the search and rescue phase, with heavy machinery brought in to excavate the site.

"The operation will carry on in a coordinated manner for as long as it takes until every single person is accounted for," said the statement.