“The department has dispatched a team of inspectors to investigate after which they will issue a preliminary report on the cause of the accident,” it said in a statement.
The department said Labour Minister Mildred Oliphant had sent her condolences to the families of those who were killed.
The house collapsed at the Meyersdal Eco Estate.
ER24 said nine people were killed and the injured were taken to hospital.
Two of the 27 builders working on the house were still missing under the rubble, spokespersonLuyanda Majija said.
“As we [were] busy searching, we discovered another three bodies,” Ekurhuleni emergency services spokesperson William Ntladi said.
“The total is nine for now, but the search is still going on. This number might change,” he said.
Earlier, Netcare 911 said five people had been killed and eight injured. Nine people were then believed to still be stuck under the rubble.
The estate confirmed the accident.
“Today, at approximately 10:30, a structure at the house of one of our residents which was undergoing alterations collapsed,” it said in a statement.
“Emergency services are still involved in rescue operations and the families of the affected workers have yet to be informed.”
Security at the upmarket estate was tight as non-residents were questioned before they were allowed access. Some were turned away.
The estate’s attorney Andrew Boerner said they were waiting for an update from emergency services.
“We ask the media to await the official statement from emergency services until such time as they have completed their rescue operation,” he said outside the gates of the upmarket estate.
“We are liaising with emergency services and providing our full co-operation to them and the contractor.”
Meyersdal Eco Estate is the property from where two giraffes were removed last month.
The giraffes were being transported on the N1 highway on a truck when one of them hit its head on a bridge and died.
Last week, the Gauteng agriculture department said the estate was being investigated over whether it had the correct permits to bring in and keep giraffes.