Forty Americans being taken off the quarantined cruise ship Diamond Princess are infected with new coronavirus, a US official says.

They are among 400 people from the US leaving the vessel docked in Japan.

Most are due to depart for the US on two government-chartered aircraft. But those carrying the virus will be admitted to Japanese hospitals.

Meanwhile, China has tightened restrictions on movement in Hubei province, the centre of the outbreak.

What is happening on the cruise ship?

The Diamond Princess has been quarantined in Japan’s port of Yokohama with some 3,700 passengers and crew on board since 3 February after a man left the ship in Hong Kong and was found to have the virus.

It has the largest cluster of coronavirus cases outside China. The Japanese authorities on Sunday said the number of new cases on board the ship had risen by 70 to 355.

The 40 Americans who are infected will receive medical treatment in Japan, Dr Anthony Fauci, Director of the National Institute of Allergy and Infectious Diseases told Face the Nation on CBS.

“Others are going to be evacuated, starting imminently, to Air Force bases in the United States,” he said.

“If people on the plane start to develop symptoms, they’ll be segregated within the plane.”

• Are coronavirus tests flawed?
• Watching loved ones die without care in Wuhan
• Why Singapore is so vulnerable to virus spread

Those entering the US will undergo a 14-day quarantine – on top of the time they have already spent confined on the ship.

“And the reason for that,” Dr Fauci added, “is that the degree of transmissibility, on that cruise ship, is essentially akin to being in a hotspot.”

NEW: Dr. Anthony Fauci of @NIAIDNews confirms to @margbrennan 40 Americans have tested positive for #Coronavirus aboard the quarantined Diamond Princess cruise ship. pic.twitter.com/b2nkiIiZpf

— Face The Nation (@FaceTheNation) February 16, 2020

Some of the Americans have declined to be evacuated by plane, preferring to wait until the ship quarantine comes to an end on 19 February.

Passenger Matt Smith, a lawyer, said he would not want to travel on a bus to the plane with possibly infected people.

we would like to just finish the quarantine on the ship as planned, decompress in a non-quarantine environment in Japan for a few days, then fly back to the U.S. pursuant to our own arrangements. What's wrong with that?

— Matthew Smith (@mjswhitebread) February 15, 2020

Other evacuation flights will repatriate residents of Israel, Hong Kong and Canada.