South African Airways (SAA) said Wednesday it was cancelling all its flights as thousands of workers vowed to press ahead with an indefinite strike the following day, after the troubled national carrier announced a major retrenchment plan.

Around 3,000 workers, including cabin crew, check-in, ticket sales, technical and ground staff, are expected to take part in the open-ended strike starting Friday, their unions said.

The looming shutdown forced SAA to announce in a late-night statement on Wednesday that it "has cancelled nearly all its domestic, regional and international flights scheduled for Friday, November 15 and Saturday, November 16".

"The airline's key objective is to minimise the impact of disruptions for its customers," it said.

Unions earlier Wednesday vowed their members would forge ahead with the strike, which the state-owned airline warned could collapse the embattled carrier.

"We are embarking on the mother of all strikes," Zazi Nsibanyoni-Mugambi, president of the South African Cabin Crew Association (SACCA) told a news conference in Johannesburg.

"We are grounding that airline on Friday," said Irvin Jim, general secretary of the National Union of Metalworkers of South Africa (NUMSA).

The unions are pressing for a three-year guarantee of job security and an eight percent across-the-board wage hike.

Pilots -- who are not taking part in the strike - have accepted a 5.9-percent increase, they said.

South African Airways workers plan an indefinite strike over job cuts and wages South African Airways workers plan an indefinite strike over job cuts and wages Photo: AFP / BEN STANSALL

The airline had announced on Monday a restructuring process that could affect 944 employees and "lead to job losses".

The airline, which employs more than 5,000 workers, is one of the biggest in Africa, with a fleet of more than 50 aircraft providing dozens of domestic, regional and European flights each day.

But the company is deep in debt, despite several government bailouts, and has not recorded a profit since 2011.

The unions blamed the SAA board and executive management for the airline's crisis.

"They have deliberately destroyed what used to be one of the world's best airlines, because of maladministration, rampant looting and corruption," they said in a statement.

SAA Chief Executive Officer Zuks Ramasia warned that the strike would "exacerbate rather than ameliorate our problem" and urged the unions to make affordable demands.

"The unions and all employees should be mindful of the current financial constraints the company is facing," she said in a statement.

She said the unions were aware that the airline's financial woes were "caused by a number of factors, including a severely distressed global airline industry."

This, she argued, had resulted in "numerous airlines retrenching staff, embarking on cost-reduction programmes, implementing wage freezes, reducing operations, or even closing down."

The airline has been surviving off government bailouts. Finance Minister Tito Mboweni announced in February that the government would reimburse the company's 9.2-billion-rand ($620-million) debt over the next three years.

South Africa is struggling to get its state-owned companies back on track after nine years of corruption and mismanagement under former president Jacob Zuma.

Analyst Daniel Silke warned in a tweet that the planned strike "may kill an airline already on its knees affecting the jobs of thousands more."