South African President Cyril Ramaphosa defended the 21-day national lock-down against the corona-virus pandemic which began on midnight Thursday, saying it is "absolutely necessary".

"This is an extreme measure we had to embark upon in response to the COVID-19 pandemic," the president said in a televised speech to the nation.

He said that the number of infections continues to grow in the country and that 1,326 people have tested positive for the virus, with 3 deaths, up to date.

"That is why we took the radical step of locking down the country for 21 days," he said.

The quarantine has disrupted people's lives, he said, "but we all know and agree that this nationwide lock-down is absolutely necessary to save the lives of thousands, even tens of thousands, of our people."

Many countries in Africa have adopted similar measures, said Ramaphosa, adding that "our own researchers and scientists have told us that our decision to lock down the country was a correct one."

Without quick actions, South Africa is only a few weeks away from a similar situation in other countries hit hard by the virus, the president said.

The lock-down, however, has been facing growing defiance. Over 1,100 people have been arrested around the country for violating lock-down rules in the past few days, said the South African Police Minister Bheki Cele.

Ramaphosa called for people's understanding of the tough measures against the raging pandemic.

"We have never experienced a situation like this before … we ask for our people's understanding that all this is being done for the good of everyone," he said.

The president said he was concerned about those who have not realized the seriousness of the disease.

"I am therefore once again calling on each and every South African to stay at home for the next 17 days," he said.

Those who infringed the rules put themselves and others at risk, helping the pandemic to spread, Ramaphosa added.

In the coming days, the government will roll out a screening, testing, tracing and medical management program, he said, adding that around 10,000 field workers will visit homes around the nation to screen residents for COVID-19 symptoms.

With mobile technology, an extensive tracing system will also be rapidly deployed to trace those who have been in contact with confirmed corona-virus cases and to monitor the geographical location of new cases in real time, said Ramaphosa.

"We are pushing ahead to implement the necessary health interventions and economic and social measures to contain the spread of the disease and alleviate its effects on our people," he said.