The World Heath Organisation (WHO) reported one confirmed and five suspected cases aboard the MV Hondius ship, which was travelling from Argentina to Cape Verde.

A 69-year-old UK national is also in intensive care in Johannesburg, South Africa. Local officials told the BBC he had the virus.

Hantavirus is usually passed to humans from rodents via their faeces, saliva or urine. It can cause severe respiratory illness. Rarely, it can be transmitted between people.

The MV Hondius is run by tour company Oceanwide Expeditions. In a statement, the operator said it is dealing with "a serious medical situation" and confirmed the three passenger deaths.

According to an itinerary on its website, MV Hondius departed from Ushuaia in southern Argentina on 20 March and completed its journey on 4 May in Cape Verde, where it is anchored outside the capital, Praia.

It is described as a 107.6m (353ft) polar cruise ship, with space for 170 passengers in 80 cabins, along with 57 crew members, 13 guides and one doctor.

Foster Mohale, a spokesperson for South Africa's health ministry, told the BBC there were about 150 tourists from various countries on board the vessel.He said a Dutch couple had died - a man, aged 70, and a woman, aged 69.

The health official said the man suddenly became ill, developing fever, headache, abdominal pain and diarrhoea. He died on arrival on the island of St Helena, a British territory in the South Atlantic.

The woman also became ill on board and was evacuated to South Africa, where she died in a Johannesburg hospital.

The third person who died was also Dutch and efforts were under way to repatriate their body, along with a guest "closely associated" with them, Oceanwide Expeditions said.

It also confirmed two crew members required urgent medical care, but authorities in Cape Verde had not given authorisation for them to disembark and go to hospital.