The people, mostly farm workers, went early on Sunday morning to measure out their plots on 67 hectares of land situated about 3km from the Sterkfontein caves in Kromdraai on the West Rand.
Building has been stopped "for now" after a meeting between the new squatters and a local council member.
Just before Beeld arrived at the scene, an ANC council member had apparently also met with the people.
More meetings were scheduled for next Sunday.
Land bought for development
The land was bought about six years ago by the West Rand district municipality to build "decent houses" for 42 families, a man from the Kromdraai Conservancy told Beeld on Sunday.
Apparently the land used to belong to a farmer, and it would have been developed for his workers. According to the man from the Kromdraai Conservancy, who didn't want to be identified, tests have shown that this land is not suitable for development due to the presence of dolomite.
"Early this morning (Sunday) there were 150 people here, measuring out plots of land. The residents are worried that the crime rate in the area could soar," he said.
Another man said they can't even develop their own land without applying to the municipality or doing an impact study.
"We're all concerned. There isn't even a sewerage system here and what will the tourists think?" said another.
Gerhard du Plooy, a resident, said the part of the land where the people want to build their shacks is the most sensitive part of the Cradle of Mankind.
"The area is a world heritage site with clear environmental guidelines for formal and informal development.
"The West Rand district municipality must ensure that these guidelines are adhered to," said Du Plooy.
According to him, the "new residents" come from as far as Midrand.
'What about our heritage?'
Simon Zulu, one of the new residents, said they are aware of the area's world heritage status.
"Yes, we know, but what about our heritage? The farmers are still living here, so where are we supposed to live?
"I just want a small piece of land where I can lay down my head, not the whole area," said Zulu.
He also said that most of the people who came to mark a piece of land are farm workers who live in the area.