OAKLAND, Calif. • The cruise ship forced to idle for days off the California coast because of a cluster of coronavirus cases aboard arrived in port Monday, and dozen of passengers began to leave for military bases where they would be quarantined or to return to their home countries.

The Grand Princess pulled into the Port of Oakland with more than 3,500 people aboard — 21 confirmed to be infected with the new virus. Passengers lining the balconies waved and some left the cabins where they had been in isolation to go on deck.

As the ship sailed under the Golden Gate Bridge to enter the harbor, passenger Karen Schwartz Dever said “everyone was hollering and clapping.”

Twenty-three people who needed acute medical care had been taken off the ship by late Monday afternoon, but it was not clear how many of them had tested positive for the virus, said Shawn Boyd, a spokesman for the California Office of Emergency Services.

Live TV footage showed at least one passenger, an older man wearing a face mask, climbing onto a stretcher and being lifted into the back of an ambulance. Officials have said the unloading will take up to three days.

“Our intent is to basically disembark about half the passengers today. Everyone will be screened initially today,” said Robert Kadlec, assistant secretary of health and human services.

Many of the nearly 240 Canadians on board left the ship after the critically ill and stood outside two tents displaying Canadian flags. Canada and the U.K. were among the countries sending chartered flights to retrieve their citizens.

U.S. passengers will be flown or bused from the port — chosen for its proximity to an airport and a military base — to bases in California, Texas and Georgia for testing and a 14-day quarantine. The ship is carrying people from 54 countries, and foreigners will be whisked home.

About 1,100 crew members, 19 of whom have tested positive for COVID-19, will be quarantined and treated aboard the ship, which will dock elsewhere after passengers are unloaded, California Gov. Gavin Newsom has said.

The virus has infected 600 people in the United States, and at least 26 have died, most in Washington state. Surgeon General Jerome Adams said communities will need to start thinking about canceling large gatherings, closing schools and letting more employees work from home, as many companies have done after an outbreak in the Seattle area.

In other hotspots around the world, the battle to halt the coronavirus brought sweeping new restrictions Monday. Italy expanded a travel ban to the entire country, Israel ordered all visitors quarantined just weeks before Passover and Easter, and Spain closed all schools in and around its capital.

Even as workers in Beijing returned to their jobs and new infections in China continued to subside, Italians struggled to navigate the rapidly changing parameters of the nation’s self-imposed lockdown.

“Now that the virus has a foothold in so many countries, the threat of a pandemic has become very real,” said World Health Organization chief Tedros Adhanom Ghebreyesus. “The great advantage we have is the decisions we all make as governments, businesses, communities, families and individuals can influence the trajectory of this epidemic.”

Worldwide, more than 113,000 people have tested positive for the disease and over 3,900 people with the virus have died, most of them in China. More than 62,000 people have already recovered. But Italy’s intensifying struggle to halt the virus’ spread emerged as a cautionary tale.

“There won’t be just a red zone,” Italian Prime Minister Giuseppe Conte said, in announcing that a lockdown covering about 16 million people in the north would be expanded to the entire country starting Tuesday.

Italian doctors celebrated one small victory after the first patient diagnosed with the illness, a 38-year-old Unilever worker, was moved out of intensive care and began breathing on his own. But the virus’ rapid spread was forcing them to operate like wartime medics, triaging patients to decide who get access to scarce ICU beds.

“Unfortunately, we’re only at the beginning,” said Dr. Massimo Galli, head of infectious disease at Milan’s Sacco hospital.

Travelers at Milan’s main train station had to sign police forms self-certifying that they are traveling for “proven work needs,’’ situations of necessity, health reasons or to return home.

Israeli Prime Minister Benjamin Netanyahu said his government has decided to quarantine anyone arriving from overseas for 14 days. The decision comes barely a month before Easter and Passover, typically a busy travel period.

In Ireland, officials canceled all St. Patrick’s Day parades in a bid to slow the virus’ spread, including the one on March 17 in Dublin that typically draws a half-million to its streets.

China reported just 40 new cases of the virus, its lowest number since Jan. 20. More than three-quarters of the country’s surviving virus patients have been released from treatment.

Passenger aboard the Grand Princess celebrate as they arrive in Oakland, Calif., on Monday. The cruise ship, which had maintained a holding pattern off the coast for days, is carrying multiple people who tested positive for COVID-19.

The Associated Press