The World Health Organisation's regional director for Africa on Friday warned the continent faced a "dramatic evolution" of the coronavirus pandemic.
Of the 47 countries in the WHO Africa region - which includes sub-Saharan Africa and Algeria - 39 nations are now affected, compared with only one a month ago, Matshidiso Rebecca Moeti told French television channel France24.
Moeti said there have been about 300 cases per day in recent days, and called for "intensified action by African countries".
"The situation is very worrying, with a dramatic evolution: an increase geographically in the number of countries and also an increase in the number of infections," Moeti said.
Cases have risen across the world's poorest continent over the past week to a total of nearly 3 500 cases and 94 deaths, according to an AFP tally that covers all of Africa.
South Africa recorded its first death due to coronavirus on Friday.
African nations have ordered curfews and lockdowns in response to the growing pandemic, amid fears that weak health infrastructure will leave the continent terribly exposed to an outbreak on the scale of virus-stricken Europe.
Moeti acknowledged that measures were being taken to contain the spread of the virus and to isolate suspected cases.
Governments have banned religious gatherings and sporting events, while schools were closed in 25 countries, she said.