Image copyright Getty Images Image caption About 3,700 people have been quarantined on board the Diamond Princess for two weeks

Britons stranded on a quarantined cruise ship in Japan have been told by the UK Foreign Office to stay onboard.

There are 74 British nationals on the Diamond Princess ship, which was quarantined on 3 February after an outbreak of coronavirus.

Passengers from other nations who had tested negative began to disembark on Wednesday.

The Foreign Office warned Britons may struggle to board a planned evacuation flight if they leave the ship.

It is understood those who get off may encounter administrative or logistical problems that prevent them from boarding the repatriation flight back to the UK.

The government said an accommodation block at Arrowe Park Hospital on the Wirral - where two previous groups were quarantined - would be used to isolate those returning from the Diamond Princess for 14 days.

"There is no risk to the public, and the hospital will continue to run as normal," the Department of Health said.

In a statement on Wednesday, the Foreign Office said it is planning an evacuation flight from Tokyo to the UK "as soon as possible".

"We hope the flight will be later this week, subject to permissions from the Japanese authorities," it said.

"However there is a chance that people who disembark will not be able to join the evacuation flight.

"We have the utmost concern for the affected Britons and strongly encourage them to register for the evacuation flight."

Image copyright PA Media Image caption Two Britons on the ship, Sally and David Abel, say they have tested positive for the virus

Meanwhile, British couple David and Sally Abel, from Northampton, remain on the cruise ship after testing positive for the virus - known as Covid-19.

Their son, Steve Abel, confirmed the diagnosis on Wednesday, following doubts over the results the previous day.

Speaking on BBC Breakfast, Steve said his father told him his diagnosis had been confirmed again by an English-speaking doctor and the couple are waiting to leave the ship for treatment.

David Abel, from Northamptonshire, previously suggested on Facebook that there had been a "massive communication error" before saying that he had "indeed tested positive for the virus".

Media playback is unsupported on your device Media caption Coronavirus cruise couple: 'They're getting messed about'

Steve said that his family were being "messed about", and added that his father was diagnosed a couple of years ago with early-onset dementia.

"He's very confused with a lot of things and he's not going to be of his normal state of mind," he said. "I just want people to realise that he's going to be saying things that he probably doesn't mean."

He said his parents have been told to stay in their room as other passengers disembark the ship.

"I don't want them separated," he said. "That's our worst fear. With my dad's early-onset dementia, he could wake up one morning, I'm not saying it's that bad at the moment, but he could wake up a bit confused so my mum needs to be there with him."

Image copyright Getty Images Image caption Passengers who had no symptoms and tested negative for the virus had their temperatures checked before leaving

Image copyright Reuters Image caption There have been more than 500 confirmed cases of the virus Covid-19 on the ship

The cruise ship operator and Japanese officials allowed some passengers to disembark the ship at 07:00 local time (22:00 GMT, Tuesday), once they were given the all-clear.

The ship was quarantined at Yokohama port earlier this month, with some 3,700 passengers and crew on board.

BBC News correspondent Laura Bicker said the first passengers who stepped off the cruise ship quickly made their way onto waiting coaches, while some even decided to take a taxi.

As of Wednesday, there were 79 new cases of the virus onboard the ship, bringing the total to 621 confirmed cases, Japanese officials said.

It is the largest cluster of cases outside China.

The US has already evacuated more than 300 of its citizens from the ship. South Korea, Canada, Australia, Israel and Hong Kong are also planning evacuations.

Image copyright Reuters Image caption The ship has been in Yokohama, a city south of Tokyo

Earlier, Japan's health minister said all passengers still on board had been tested for the virus and those who had tested negative would start leaving the ship on Wednesday.

Another British passenger on board the ship, Elaine Spencer, said she had been "very disappointed" with the UK government's initial response and said a rescue flight should have been organised sooner.

She told Radio 4's Today programme that British passengers who wanted to get on the rescue flight had to sign an agreement that they would go into quarantine for 14 days on their return to the UK.

"I need to go home, I want to see my family but obviously it's going to be another 14 days (after the flight). I wish that they'd decided to do this last week."

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It comes as Alan Steele, a British honeymooner diagnosed with coronavirus on the cruise ship, announced on Facebook that he had left hospital.

Mr Steele said he is in a hotel in Yokohama and has been told he will need to spend two weeks in quarantine when he returns to the UK.

Covid-19 has now claimed 2,004 lives in China, according to the latest Chinese data released on Wednesday.

There have been 74,185 confirmed infections recorded in mainland China and about 700 cases in other countries.

Irish foreign minister Simon Coveney confirmed two out of six Irish passengers on the Princess Diamond tested positive for the virus and are being treated in hospital in Japan.

Mr Coveney said the passengers have dual citizenship with another EU member state and did not normally live in Ireland - but that the Irish embassy in Tokyo was in contact with them.

The president of Princess Cruises, Jan Swartz, said the company has sent more doctors and nurses on to the ship.

The Foreign Office is advising affected British nationals to call the British embassy in Tokyo on +81 3 5211 1100.

In the UK, a total of 5,216 people had been tested for cornoavirus, as of Wednesday at 14:00 GMT. Only nine people have tested positive and the rest have been confirmed negative.

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