“Thirteen people were arrested. Strikers were burning rubble and dustbins at several locations in the CBD (central business district) as well as some of the stalls along the route were robbed,” said police spokesman Captain Federick van Wyk.

Damage to cars, street trader stands and shopfronts and the fires will be studied on the city’s surveillance camera footage, municipal spokeswoman Kylie Hatton told AFP.

“The levels of violence were unacceptably high,” she said, adding that non-striking staff had also been intimidated by those who had walked off the job.

“We have had a number of reports of intimidation right across the city.”

A court injunction will be sought to stop the strike as a result of the violence with some 1,200 people taking part in Tuesday’s march over demands for an 18-percent wage hike, the city said.

Zimbabwean street trader Solomon Shumbanhete was robbed of curios worth 1,000 rands ($140, 97 euros) as shouting marchers moved toward the civic centre to hand a petition to the South African Local Government Association (Salga).

“It was very bad — they weren’t supposed to harrass people doing something for tourism,” he said.

The strike has affected refuse collection, the city said.

The union called the strike Monday for nearly 200,000 workers in the municipal and water sectors with an independent union set to join on Friday.

Salga has offered a six percent raise with the union’s 18 percent demand more than three times the rate of headline inflation of five percent in June.

The mid-year winter months of contract negotiations are known as “strike season” in South Africa with walkouts in some major industries, including coal and gold mining, oil refineries and engineering, since June.

The arrested marchers face fines of 500 rands, said Van Wyk.