South Africa is holding more than 1,700 people on a cruise liner and a cargo vessel off the coast of Cape Town because of coronavirus.
A crew member of cargo ship MV Corona is suspected to have the virus.
He had been on a flight with six other people, who then boarded Italian-flagged cruise liner MV Aidamira.
South Africa has 116 cases of coronavirus and President Cyril Ramaphosa has declared a state of disaster, restricting travel.
Nearly half – 35 out of 72 – of South Africa’s land border crossings were closed on Monday, along with two of its eight sea ports.
The MV Aidamira, with 1,240 passengers and 486 crew on board, had returned to Cape Town from Namibia’s Walvis Bay.
The ship is mainly carrying German and Austrian nationals, though other nationalities are also thought to be on board, reports the BBC’s Pumza Fihlani from South Africa.
Health authorities say they are awaiting coronavirus test results from six people on the cruise liner.
“We are prioritising the testing,” health ministry spokesman Popo Maja told the BBC.
None of the passengers or crew on the cruise liner are reported to be displaying symptoms of coronavirus, according to a spokesman for the company.
The MV Corona left Cape Town on 11 March but the ship’s master requested to return after the patient started to show symptoms of the virus, news agency Reuters reports.
The crew member has since been placed in isolation on-board the MV Corona, along with another crew member who was on the same flight from Turkey.
Authorities are working on tracing all the people the suspected cases came into contact with.
Meanwhile, all schools in South Africa have closed from Wednesday.
Foreigners travelling from badly affected countries are also barred from entry into the country.
The concern is that the virus may spread fast in poor, crowded neighbourhoods.