The country has already been under lockdown for two weeks and it was due to be lifted in a week.

The president has said it will be extended because evidence suggested it was already limiting Covid-19's spread.

The Democratic Alliance (DA) said it was a "great mistake to think in terms of lives versus livelihoods".

"Each death resulting from the virus is a tragedy. But so is each death resulting from caged citizens and frustrated law enforcers, and so is each victim of home violence. And each malnourished child. And each newly unemployed South African," the party said in a statement.

"We would prefer a gradual phasing out of the current lockdown over the coming weeks."

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In a televised address to the nation on Thursday evening, President Cyril Ramaphosa said the decision to extend the strict restrictions had not been taken lightly.

"I have to ask you to make even greater sacrifices so that our country may survive this crisis and so that tens of thousands of lives may be saved," he said.

Media captionCoronavirus in South Africa: Lockdown fears for Johannesburg residents

He also announced that senior politicians would donate a third of their salaries to help those worst affected by the pandemic and urged business leaders to do the same.

South Africa has recorded 1,934 confirmed cases of Covid-19, the respiratory illness caused by coronavirus, including 18 deaths.

The country has some of the most stringent lockdown restrictions in the world - no jogging outside, no sales of alcohol or cigarettes, no dog-walking, no leaving home except for essential trips and prison or heavy fines for law-breaking.

South Africa, which is the continent's most-industrialised nation, has acted fast and aggressively to tackle the virus, sending out health workers to do door-to-door screening.

But Mr Ramaphosa acknowledged that far more testing was needed to be sure that the virus was not spreading undetected, reports the BBC's Andrew Harding from Johannesburg.

On Thursday, the World Bank said sub-Saharan Africa would suffer its first recession for 25 years as a consequence of the coronavirus outbreak.

Before the lockdown began, the government announced a series of measures to cushion the economic effects of the lockdown, including a solidarity fund to help small businesses.

However, the DA said more needed to be taken to ensure that South Africans would have jobs to return to once the pandemic was over.