But Michel Yao, head of emergency operations for WHO Africa, said that was a tentative projection which could change and noted worst-case predictions for the Ebola outbreak had not come true because people changed behaviour in time.
"This is still to be fine-tuned," he told a media teleconference. "It's difficult to make a long-term estimation because the context changes too much and also public health measures when they are fully implemented, they can actually have an impact."
The world's poorest continent has seen more than 17,000 confirmed cases of the COVID-19 disease and about 900 deaths so far - relatively little compared to some other regions.
But there are fears that could balloon and overwhelm shaky health services.
"We are concerned that the virus continues to spread geographically, within countries," said Matshidiso Moeti, director for WHO's Africa region, which comprises 46 sub-Saharan nations and Algeria.
"The numbers continue to increase every day."