Thousands of South African transport workers went on strike on Monday at logistics group Transnet, threatening to cripple rail, fuel pipelines and port operations in Africa's biggest economy.

The strike - the latest in a series of public protests ahead of next month's soccer World Cup - could affect coal and iron-ore exports, fuel distribution, and shipping.

Power utility Eskom said the strike, which began after failed wage talks, would have no impact on the transport of coal used to power its plants, as only small amounts of coal were carried by rail, with the rest supplied by conveyor belts directly from mines.

Transnet does not run passenger train services,

The South African Transport and Allied Workers Union (Satawu) said it expected all of its 20 000 members to strike. Another union, the United Transport and Allied Trade Union (Utatu) has urged its members to consider Transnet's latest pay offer and to report for duty on Monday.

If Utatu's members reject the offer, the union said it would join the strike by Wednesday. The two unions represent 85% of Transnet's workforce of about 54 000 people.

Both unions want a 15% pay increase. Transnet has now offered 11%.

"We can keep this strike going as long as the employer has not met our demands," said Joseph Dube, Satawu's secretary for the KwaZulu Natal province.

Fifteen people were hurt when police fired rubber bullets at them in the port city of Durban after they failed to follow a police order to disperse, the SAPA news agency said.

Transnet and coal, iron-ore, ferrochrome and fuel producers, said they were confident they could supply customers for days due to built up stocks at the ports.

"The strike will not have a material immediate impact on our exports," said Pranill Ramchander, an Anglo American spokesman.

The group's thermal coal unit is the country's biggest coal exporter. South Africa exports most of its coal to power stations in Europe, but increasingly to Asia as well.

For now, operations at Richards Bay Coal Terminal, the world's largest coal export terminal, have been running as normal, Chief Executive Raymond Chirwa said.

"Depending on ship arrivals, our stocks could last us for three to four weeks," he said.

Kumba Iron Ore, also an Anglo unit, said the company had sufficient stocks at Saldanha port to keep loading vessels for at least seven days.

If the strike is prolonged, it could have a serious impact on the country's ferrochrome industry, the world's largest. Hernic Ferrochrome, a unit of Japan's Mitsubishi Corporation, relies on Transnet for 75% of its transports.

Freshgold SA Exports, which ships fresh produce out of the country said its operations were being hit.

"The strike has physically halted our container loadings from this morning ... if it's a week the impact will be quite severe," said Freshgold MD Pieter von Maltitz.