A wildcat strike by rubbish collectors continued on Tuesday in Johannesburg as rotten rubbish were piling up, prompting authorities to warn against a potential health catastrophe.

Pikitup workers affiliated to the South African Municipal Workers Union have been on an unprotected strike for more than a month.

The striking workers are demanding a salary increase and the removal of their boss Amanda Nair whom they accuse of corruption.

Health officials have discovered dormant bubonic plague in a dead rat near Midrand, Johannesburg, where tons of rotten rubbish were uncollected.

The National Institute of Communicable Diseases (NICD) has called for an urgent intervention as people are exposed to health risks, especially in informal settlements, as rubbish heaps around the City of Johannesburg mount.

Many residents keep complaining that sticking smell is so overwhelming that they smell it in their sleep.

NICD's Professor John Frean said flies and roddents converging on the rotten rubbish can transmit germs mechanically, and people handling the rubbish or playing in it, as children might do, might be exposed.

The Gauteng Health Department is appealing to have the waste cleaned up.

"We understand the workers' issues and that they are central. We will never downplay those issues. However, workers must have a full understanding of the impact and the implications of the uncollected rubbish over such a prolonged period of time," said Qedani Mahlangu of the department.

The opposition Democratic Alliance (DA) said it has written to the speaker of the Johannesburg Metro, Constance Bapela, requesting her to urgently convene a special council meeting to discuss the strike.