Johannesburg (CNN) South Africa will enforce a three-week lockdown over coronavirus, President Cyril Ramaphosa announced Monday.

In a televised address to the nation, Ramaphosa said the 21-day lockdown will begin at midnight Thursday and he called on the country to "urgently and dramatically" escalate its response.

"Immediate, swift and extraordinary action is required if we are to avoid human costs of this virus," said Ramaphosa, adding that if the nation failed to act swiftly, it could face "a human catastrophe of enormous proportions."

In the week since the country declared a state of national disaster, the number of confirmed cases has increased sixfold, Ramaphosa said, especially troubling in a country with a large immune-suppressed population of HIV and tuberculosis suffers.

"The action we are taking now will have lasting economic costs," said Ramaphosa. "But we are sure that the cost of not acting now will be far greater."