Some 70,000 workers at oil refineries and related industries on Monday joined a week-old strike in South Africa, their union said, raising fears of potential fuel shortages.

The Chemical, Energy, Paper, Printing, Wood and Allied Workers Union (CEPPWAWU) said refineries had ground to a halt as workers downed tools to march through the streets of the country's industrial centres demanding a minimum salary of 6,000 rand ($890, 630 euros) a month.

"It's clearly going to have a major impact on the supply of fuel," union spokesman John Appolis told AFP.

But the country's largest crude refinery, Sapref, said it would not shut down, the Sapa news agency reported.

"Although CEPPWAWU has called for a national strike, Sapref does not anticipate that they will need to shut down," said Margaret Rowe, spokeswoman for the Shell and BP joint venture.

"Sapref intends to continue operating for as long as it is safe to do so."

CEPPWAWU is demanding increases of 11 to 13 percent, a 40-hour work week and six months' paid maternity leave. Employers are offering raises of four to seven percent. The work week currently runs up to 42 hours per week.

The strike involves the pharmaceutical, industrial chemicals, grocery and pulp and paper industries.

The latest labour action comes on top of a stayaway by more than 110,000 engineers and metalworkers, who downed tools last week demanding a 13 percent raise.

Inflation in South Africa was at 4.6 percent in May.

The mid-year winter months are known as "strike season" in South Africa, where many contracts expire at the end of the fiscal year on June 30.

Wage negotiations are currently ongoing in the key coal and gold mining sectors, with coal miners due to resume talks with employers next week.