Kenya, Ethiopia, Sudan and Guinea all confirmed their first cases of the new Coronavirus on Friday, giving the disease a foothold in 18 countries on the African continent.
Africa had so far largely been spared the rapid spread of COVID-19, which has infected at least 127,000 and killed 4,700 worldwide.
Most of Africa's reported cases were foreigners or people who had travelled abroad. Rapid testing and quarantines have been put in place to limit transmission.
But concerns are growing about the continent's ability to handle the disease.
Cases have been reported in Morocco, Tunisia, Egypt, Algeria, Senegal, Togo, Cameroon, Burkina Faso, Democratic Republic of Congo, South Africa, Nigeria, Cote D'Ivoire, Gabon, Ghana, Guinea, Sudan, Kenya and Ethiopia. Most of the countries' totals are still in single figures.
Kenya is the richest economy in East Africa and a hub for global firms and the United Nations. Ethiopia is Africa's second-most populous nation, with 109 million citizens. Both Addis Ababa and Nairobi are regional transit hubs.
In the Kenyan capital Nairobi, authorities banned all major public events and said they would restrict foreign travel. The mayor of Ethiopia's capital Addis Ababa urged citizens to avoid close personal contact but the health minister said there were no plans to cancel flights.
Kenyan Health Minister Mutahi Kagwe said their first case, a 27-year-old Kenyan, was diagnosed on Thursday after travelling home via London on March 5.
He said the government had traced most of the people she had been in contact with, including fellow passengers on her flight, and a government response team would monitor their temperatures for the next two weeks.
The Ethiopian case was a 48-year old Japanese national who arrived in Ethiopia on March 4, the health ministry said.
Guinea's first case was an employee of the European Union (EU) delegation who had self-isolated after she felt ill upon returning from Europe, the EU delegation said.
Sudan's first confirmed Coronavirus case was a man who died on Thursday in the Sudanese capital Khartoum, the health ministry said. He had visited the United Arab Emirates in the first week of March.
Kagwe said the government had suspended all public gatherings, sporting events, open-air religious meetings and events of a huge public nature. Schools will remain open but inter-school events are suspended.
Public transport operators must install hand sanitizers in their vehicles and clean them regularly, Kagwe said, while foreign travel would be restricted.
Soon after the announcement, shoppers in one Nairobi supermarket were buying up cart loads of staples like maize flour and water as well as hand sanitizers and soap.
Kenya Airways suspended flights to China last month and on Thursday added Rome and Geneva to the list of suspended destinations.
Kenya, dependent on Asian imports, has seen disruptions to its supply chain and a decline in tourism, an important source of hard currency and jobs.
"We are going to be hit badly," Tourism Minister Najib Balala told journalists.
The Nairobi Securities Exchange halted trading in the afternoon after the main NSE 20 share index dropped by more than 5% following the news.
Also in East Africa, the island nation of Mauritius, whose economy depends on tourism and financial services, said it was seeking to mitigate the effects of the virus by offering liquidity to banks to support struggling firms and cutting the cash reserve requirements for banks. It has not yet reported any cases of COVID-19.