From the Rose Garden, Trump said, "I am officially declaring a national emergency," unleashing as much as $50 billion for state and local governments to respond to the crisis.
Trump also announced a range of executive actions, including a new public-private partnership to expand coronavirus testing capabilities with drive-through locations, as Washington tries to subdue the new virus whose spread is roiling markets, shuttering institutions and disrupting the lives of everyday Americans.
But he denied any responsibility for delays in making testing available as his administration has come under criticism for being too slow to respond.
Trump said, "I don't take responsibility at all" for the slow rollout of testing.
As the House prepared to vote late Friday, Speaker Nancy Pelosi trumpeted the hard-fought package that will provide free testing, sick pay for workers, enhanced unemployment benefits and bolstered food programs.
"We did what we said we were going to do: Put families first," said Pelosi, flanked by Democratic lawmakers, including many freshmen. The House passed the bill after midnight on a bipartisan vote, 363-40. It now goes to the Senate.
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Trump's tweet of approval instilled fresh energy in the package, all but ensuring that wary Republicans would join with a robust vote.
"I fully support H.R. 6201: Families First CoronaVirus Response Act," Trump wrote.
I fully support H.R. 6201: Families First CoronaVirus Response Act, which will be voted on in the House this evening. This Bill will follow my direction for free CoronaVirus tests, and paid sick leave for our impacted American workers. I have directed....— Donald J. Trump (@realDonaldTrump) March 14, 2020
"I encourage all Republicans and Democrats to come together and VOTE YES!" He added, "Look forward to signing the final Bill, ASAP!"
The crush of late-day activity capped a tumultuous week in Washington as the fast-moving virus left ordinary Americans suddenly navigating self-quarantines, school closures and a changed way of life.
The White House was under enormous pressure, dealing with the crisis on multiple fronts as it encroached ever closer on the president.
Trump has been known to flout public health advice - and was eagerly shaking hands during the more than hour-long afternoon event - but acknowledged he "most likely" will be tested soon after exposures to individuals who have tested positive for the virus. The White House physician indicated later his interactions were low-risk and testing is not necessary.
Still, Trump said officials don't want people taking the test unless they have certain symptoms. "We don't want people without symptoms to go and do that test," Trump said, adding, "It's totally unnecessary."
Additionally, Trump took a number of other actions to bolster energy markets, ease the financial burden for Americans with student loans and give medical professionals additional "flexibility" in treating patients during the public health crisis.
"Through a very collective action and shared sacrifice, national determination, we will overcome the threat of the virus," Trump said.
Central to the aid package from Congress, which builds on an emergency $8.3 billion measure approved last week, are the free testing, sick pay and family leave provisions.
For most people, the new coronavirus causes only mild or moderate symptoms, such as fever and cough. For some, especially older adults and people with existing health problems, it can cause more severe illness, including pneumonia.
The vast majority of people recover. According to the World Health Organization, people with mild illness recover in about two weeks, while those with more severe illness may take three to six weeks to be over it.
Trump said he was gratified that Brazilian President Jair Bolsonaro tested negative for the virus, after the pair sat next to each other for an extended period of time last weekend at Trump's Mar-a-Lago club. A senior aide to Bolsonaro tested positive.
The White House physician said in a memo late Friday that Trump was also exposed to a second guest at the club dinner, "sharing the table with the president," who has since tested positive for the virus. Still despite the incidents, the physician said Trump had only "LOW risk" interactions and testing "is not currently indicated."
Trump's daughter, Ivanka Trump, worked from home Friday after meeting with Australian Home Affairs Minister Peter Dutton, now in isolation at a hospital after testing positive for the coronavirus. White House spokesman Judd Deere said she was evaluated by the White House Medical Unit.
Attorney General William Barr, who also met with the Australian official, stayed home Friday, though he "felt great and wasn't showing any symptoms," according to his spokeswoman Kerri Kupec.
Several lawmakers, including some close to Trump, have also been exposed to people who tested positive for the virus, and are self-isolating.
RELATED: Trump says he'll likely be tested for COVID-19 'fairly soon'
Among them are Republican Sens. Lindsey Graham and Rick Scott, who were at Trump's club on the weekend. Graham announced Friday that he also met with the Australian official who has now tested positive. And GOP Sen. Ted Cruz of Texas, who had previously isolated himself after a potential exposure at a conservative conference in Washington, said Friday he met with a Spanish official and is now self-quarantining.
Hospitals welcomed Trump's emergency declaration, which they and lawmakers in Congress had been requesting. It allows the Health and Human Services Department to temporarily waive certain federal rules that can make it harder for hospitals and other health care facilities to respond to an emergency.
RELATED: Symptoms, prevention, and how to prepare for a COVID-19 outbreak in the US
The American Medical Association said the emergency declaration would help ensure America's health care system has sufficient resources to properly respond to the ongoing outbreak.
Dr. Anthony Fauci, infectious disease chief at the National Institutes of Health, said more tests would be available over the next week, but warned, "We still have a long way to go."
Trump's national emergency declaration: What you need to know
WHY IS IT IMPORTANT?
The declaration begins the process under which state and tribal governments can get access to federal dollars as they respond to the spread of the virus. The declaration helps ensure that the government is leveraging resources to help avert the human suffering and loss of income that would occur in a pandemic.
HOW CAN STATES ACCESS THE FEDERAL MONEY?
Governors will still need to ask for a "major disaster" declaration for their states, and Trump has encouraged all governors and tribal leaders to consider making such a request.
HOW MUCH MONEY IS AVAILABLE?
Most disaster assistance from the federal government is made available from the Federal Emergency Management Agency through a Disaster Relief Fund that had a $41.6 billion balance at the end of February. The bulk of the money is used to reimburse state and local governments when disaster costs are too much for them to absorb. States generally cover 25% of the cost with the federal government paying 75%.
HAVE PRESIDENTS PREVIOUSLY USED EMERGENCY DECLARATIONS TO CONFRONT INFECTIOUS DISEASES?
Yes, under President Bill Clinton in 2000, the detection of West Nile virus in New York and New Jersey was used as the basis of an emergency declaration.
WHERE CAN FEDERAL ASSISTANCE HELP?
The federal funding can help in a range of areas, such as providing temporary medical facilities when existing ones are overloaded; providing for food, water, ice and other consumable supplies; helping communicate health and safety information to the public; and transporting supplies and people.