By Doina Chiacu and Maria Caspani

WASHINGTON/NEW YORK (Reuters) – The streets of major U.S. cities were eerily empty on Tuesday morning after officials from President Donald Trump on down stepped up warnings about the coronavirus pandemic, while the number of cases mushroomed and deaths topped 80.

Millions of Americans hunkered down in their homes instead of commuting to work or school. New York and other major cities escalated “social distancing” policies by closing schools, bars, restaurants and theaters.

Officials in six San Francisco Bay Area counties on Monday ordered residents to stay at home for all but the most crucial outings until April 7. That directive came a day after California Governor Gavin Newsom urged adults older than 65, and their caretakers, to remain indoors whether or not they have underlying health conditions.

It was St. Patrick’s Day but the mood was sober, not joyous, after traditional parades and parties celebrating the Irish heritage of many Americans were cancelled across the country.

Financial markets will look to stabilize after the stock market suffered a historic loss on Monday. The S&P 500 tumbled 12 percent, its worst single-day loss since the stock market crash of 1987.

But politics will proceed mostly as scheduled in three of four states that have primary elections on Tuesday to select a Democratic presidential candidate to challenge Trump in the November general elections.

Democratic candidates Joe Biden and Bernie Sanders square off in Florida, Illinois and Arizona, but Ohio officials canceled their primary due to coronavirus fears hours before the vote was to begin.

The tally of confirmed U.S. cases has multiplied quickly over the past few weeks, surpassing 4,600 and prompting fears American hospitals might soon be overwhelmed, as Italian medical centers have been strained to the breaking point.

At least 83 people in the United States had died of the virus, as of Monday, according to Johns Hopkins University and various state and local public health agencies, with the hardest-hit state, Washington, accounting for the bulk of the fatalities, including six more announced on Monday.

The United States has lagged behind other industrializednations in its ability to test for the novel coronavirus. Inearly March, the Trump administration said close to one milliontests would soon be available and anyone who needed a test wouldget one, a promise it failed to keep.

After previously downplaying the danger and declaring the situation under control, the White House urged Americans on Monday to avoid gatherings of more than 10 people and called for closing bars, restaurants and other venues in states where local virus transmission exists.

The president’s change in tone followed newly urgent messaging from governors and mayors across the country who have taking their own drastic measures.

The states of New Jersey, New York and Connecticut struck a regional agreement to close all movie theaters, casinos and gyms as of 8 p.m. Monday (0000 GMT). Restaurants and bars in the three states – where more than 22 million people live – will serve takeout and delivery only.

Deborah Birx, White House coronavirus response coordinator, would not say whether the Trump administration was close to issuing some sort of domestic travel restriction.

“We’re looking very carefully at the data every day and that’s why you see this escalation in guidelines from the president,” she said on Fox News.

She said integrating data and understanding how the new outbreaks are occurring – from travel between states, or within states – is crucial to formulating the response and updating guidelines.

“As we track down these outbreaks, if we see that that is happening from flight travel, then I think the president will react but we don’t have enough information right now to suggest that,” she said.

Asked if people were getting sick on airplanes, Birx said, “We don’t know.”

Birx also said authorities remain focused on ramping up testing in communities “so that people in the hospitals are not overrun by continuous need for diagnosis.”

In one ray of positive news, actor Tom Hanks and wife Rita Wilson, who tested positive for coronavirus last week, are out of a hospital in Australia, according to a video posted by their son Chet on Instagram.

“They’re still self-quarantined obviously, but they are feeling a lot better,” he said.

(Reporting by Doina Chiucu and Maria Caspani; Writing by Daniel Trotta; Editing by Alistair Bell)