South African police fired rubber bullets at striking truck drivers on Monday after they stoned vehicles transporting goods in Johannesburg and pulled drivers out of their cabs.
Truckers, whose labour action started at the weekend, are threatening a strike they say will hurt Africa's largest economy. Industry officials said there has been no major impact yet, with companies lining up alternative transport.
Police said about 10 trucks were vandalised.
Johannesburg metro police spokesman Wayne Minnaar said: We advise that truck drivers avoid downtown Johannesburg because things are violent there, the SAPA news agency reported.
The South African Allied Transport Worker's Union (SATAWU), the biggest body in the trucking industry and three other unions that in total represent more than 30,000 truckers, are demanding a 20 percent salary increase over the next two years, housing allowances and shorter working hours.
The strike is going to continue indefinitely until the demands are met, SATAWU first vice president June Dube told Reuters. All sectors of the South African economy and neighbouring states will be affected.
Trucking industry group Road Freight Association has offered a 7.5 percent rise this year and 7.5 percent next year.
The strike has not had any major impact yet on transport, said Magretia Brown-Engelbrecht, labour relations manager with the Road Freight Association. We will be having a meeting with the unions on Tuesday, she said.