People who had been kept aboard a cruise ship owned by Carnival Corp may disembark soon, after tests showed that a passenger who came down with fever and respiratory symptoms didn't have the new coronavirus.

Carnival's Italian Costa Crociere unit said passengers can now leave the ship, which had been in lockdown in a port near Rome, though the vessel will not depart for the next leg of its journey until Friday evening.

LUCA BRUNO/AP People who had been kept aboard a cruise ship owned by Carnival Corp may disembark soon, after tests showed that a passenger who came down with fever and respiratory symptoms didn't have the new coronavirus. (File photo)

The Italian Health Ministry said that two suspect cases tested negative for coronavirus.

Carnival Corp shares fell as much as 11 per cent in London and traded down 3.8 per cent in New York.

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The World Health Organisation on Friday declared the coronavirus outbreak an international emergency, allowing global authorities to help countries with less robust health systems.

Hundreds of passengers waiting to get on board in the port of Civitavecchia near Rome will spend the night in hotels, the Port Authority said via speaker-phones at the dock.

Tests showed that the two passengers had A/H1N1 flu, Italy's health ministry said. The ship is not subject to any medical restrictions, according to a ministry statement.

ROBERTO MONALDO/AP The Italian Health Ministry said that two suspect cases tested negative for coronavirus.

Italian Prime Minister Giuseppe Conte said that two coronavirus patients who weren't aboard are currently in isolation in a Rome hospital and all flights to and from China have been halted.

The two Chinese tourists have been under observation since Wednesday, Conte said in a press conference in Rome, adding that there is no reason to panic. Italy is well prepared to cope with the emergency, he said.

Italian media reported that passengers had been protesting the lockdown of the ship and lack of information.

Throughout the afternoon, the vessel was the only ship docked in the city's port, with a limited security presence around it.

Passengers were seen walking on the decks while empty buses waited below for an eventual disembarkation. Soft jazz could be heard playing on board during the day.

"There's no panic, we only are very sorry we couldn't see Rome this morning, especially since the weather is so beautiful," Agata Wieczorek, 36, a Polish tourist on the cruise with her husband and three children, said by phone.

The vessel was bound for La Spezia in the Liguria region, with 1,000 crew and 6,000 passengers, 750 of whom came from China, a port spokesman said. It will skip the next stage and go directly to the northern port of Savona.