Updated at 8:30 p.m. with the president declaring a “strong travel advisory” in lieu of quarantine for nation’s largest city.

WASHINGTON — President Donald Trump floated the possibility of an “enforceable quarantine” for New York City and surrounding areas on Saturday, backing off hours later after New York Gov. Andrew Cuomo called the idea implausible and a “federal declaration of war.”

“This would be an enforceable quarantine. And, you know, I’d rather not do it, but we may need it," Trump said Saturday morning. Cuomo immediate rejected the idea and by afternoon, warned that such a lock down of the nation’s largest city, site of half the U.S. COVID-19 cases, would create “chaos and mayhem."

“I don’t think it is plausible. I don’t think it is legal,” he said on CNN.

A few hours later, Trump announced that after consulting with his coronavirus task force, the Centers for Disease Control “issue a strong Travel Advisory...A quarantine will not be necessary.”

The CDC’s advisory, issued Saturday night, “urges residents of New York, New Jersey, and Connecticut to refrain from non-essential domestic travel for 14 days effective immediately.”

Many states, counties and cities have issued stay-at-home orders but an order on the scale Trump suggested would be far more sweeping than any step yet taken in the United States to slow the contagion. In China, a two-month lockdown in Wuhan, where the new coronavirus emerged, began easing only on Saturday.

In Texas, Gov. Greg Abbott issued an executive order on Thursday requiring a 14-day self-quarantine for anyone flying into the state from New York, New Jersey, Connecticut or New Orleans.

“A lot of the states that are infected — they’ve asked me if I’d look at it so we’re going to look at it," Trump told reporters before boarding Air Force One for a short flight to Norfolk, Va., for a visit to a Navy hospital ship headed to New York. “It would be for a short time."

Cuomo’s immediate reaction: No thanks.

“I don’t like the sound of it," he told reporters in Albany. “I don’t know how that could be legally enforceable, and from a medical point of view I don’t know what you would be accomplishing.”

....Federal Government. A quarantine will not be necessary. Full details will be released by CDC tonight. Thank you! — Donald J. Trump (@realDonaldTrump) March 29, 2020

Gov. Andrew Cuomo on President Trump saying he’s considering a possible short-term quarantine for New York: “I don't know how that could be legally enforceable. … Not even understanding what it is, I don't like the sound of it.” https://t.co/FZIPOnKW0h pic.twitter.com/RFD7r0xaEM — CNN Newsroom (@CNNnewsroom) March 28, 2020

Trump added that a federal quarantine order would not include closure of the subway system in the nation’s largest city, reflecting that the lock down he envisioned was aimed at stopping the spread beyond the tri-state area, rather than protecting residents of the city itself.

“Some people would like to see New York quarantined because it’s a hot spot — New York, New Jersey maybe one or two other places, certain parts of Connecticut quarantined,” Trump said at the White House before boarding Marine One headed to Joint Base Andrews, Md. “I’m thinking about that right now. We might not have to do it but there’s a possibility that sometime today we’ll do a quarantine — short term — two weeks for New York, probably New Jersey, certain parts of Connecticut.”

Trump indicated he was considering a quarantine because of complaints from Florida Gov. Ron DeSantis about New Yorkers traveling to his state and spreading the contagion.

“Restrict travel," Trump said, providing a broad outline of the idea. "Because they’re having problems down in Florida. A lot of New Yorkers are going down. We don’t want that. Heavily infected.”

He added that “this would be an enforceable quarantine. And, you know, I’d rather not do it, but we may need it.”

I am giving consideration to a QUARANTINE of developing “hot spots”, New York, New Jersey, and Connecticut. A decision will be made, one way or another, shortly. — Donald J. Trump (@realDonaldTrump) March 28, 2020

On Friday, the House approved, and Trump signed, a $2.2 trillion rescue package, unprecedented in size and scope, that includes bailouts for airlines, direct payments of $1,200 to most taxpayers, and extended unemployment benefits.

Lawmakers predicted that far more will be needed to restart an economy reeling from the effects of a pandemic that left millions jobless in a matter of weeks.

A quarantine on a city of 8.6 million would be unprecedented in the United States, and could be hard to enforce.

Manhattan accounts for only about 1.6 million of the city’s population. It’s connected to the other five boroughs, and to New Jersey, by bridges, tunnels and ferries. Staten Island has ferry and bridge connections. Queens, Brooklyn and the Bronx would be much harder to isolate and in any case, as Cuomo noted, residents rely on deliveries of food and other supplies.

New York’s metropolitan area is home to 23 million people in New York, New Jersey and Connecticut who live close enough to commute for work, though it’s unclear how far out the possible quarantine zone would extend. Stock markets based in Manhattan that have seen unprecedented volatility in recent weeks would likely be disrupted.