Structural collapse of a large home in an upscale Johannesburg, South Africa development that killed seven now is under investigation. Officials cite lack of site safety supervision.

South African safety officials say the probe into the Aug. 18 collapse of a large home under renovation near Johannesburg that killed seven workers, including the site manager, won't be complete until November, but critics point to a continuing lack of site supervision on projects.

The country's Dept. of Labor has set up an inquiry into the collapse at the upscale Meyersdal Eco-Estate, a housing development located in a nature reserve.

Initial reports from survivors, the structure's engineer and the client indicate that the removal of two pillars in the house caused a concrete slab to fall on the workers.

Johannesburg-based contractor Romicon declined to respond to emailed inquiries about the accident, noting in a statement that it "will be assisting with contributions for the funerals.”

Municipal officials with jurisdiction over Meyersdal said last month the renovation was illegal because “no plans were submitted," says a spokesman.

Master Builders South Africa (MBSA), a federation of registered contractors and related building-industry firms, said the collapse of this and many others previous buildings is due to a “lack of skilled supervision of the construction site.”

“We should not be surprised if more structures collapse and more people are killed,” said MBSA Chief Executive Officer Tumeleng Dlamini. “Signs have been building over a period of time, considering that the housing sector is a depressed industry right now operating under very challenging economic conditions.”

Dlamini said that, because 70% of the entire workforce in South Africa’s building sector is either unskilled or semi-skilled, “if you don’t have the necessary skills supervising the workforce ... then you have an accident waiting to happen.”

The National Home Builders Registration Council, a statutory body that protects homebuyers and regulates the homebuilding industry, said, in early September, that it has launched separate investigations into the collapse of the house but confirmed that the contractor, Romicon, is a registered firm.

Last February, the council fined South Africa property developer Woodglaze Trading $128,000 for starting construction of 96 residential houses before being approved by the council.