Speaking during an afternoon Rose Garden event, Trump gathered American retail executives to announce they were donating resources to institute drive-through testing at locations across the country, collected on a new online portal.
And he said he was waiving interest on student loans and purchasing more crude oil for the US strategic reserve to fill it "right to the top."
Trump's announcement concluded a week that saw cancellations and restrictions that have altered life for nearly every American as the virus spreads to nearly every US state.
After a widely derided prime-time address on Wednesday that preceded a historic plunge in stocks, Trump faced pressure to demonstrate a handle on the crisis.
And though he announced several new steps Friday, Trump said during a question-and-answer session that he did not feel responsible for early testing failures that health experts have said led to further spread.
"I don't take responsibility at all," he said, insisting the problems that led to slow test distribution were the fault of previous administrations.
He said the emergency action would "unleash the full power of the federal government."
Trump is declaring both a national emergency and invoking the Stafford Act, which gives access to additional funding, according to a source familiar with his decision. The national emergency gives access to additional authorities.
Even as he was announcing a scaling up of testing capacity for coronavirus, however, the President said Friday he did not believe all Americans should rush to be tested.
"We don't want people to take a test if we feel that they shouldn't be doing it. And we don't want everybody running out and taking -- only if you have certain symptoms," he said in the Rose Garden.
Trump, who began his remarks giving himself plaudits for his response to the outbreak, still appeared to believe the spread could be limited and that not every person in the country would require access to tests.
"We don't want everybody taking this test, it's totally unnecessary," he said.
But he also suggested the virus would worsen before eventually improving, though he used imprecise terms to explain his thinking.
"It could get worse. The next eight weeks are critical," Trump said. "Some of the doctors say it will wash through, it will flow through. Interesting terms."
Trump has been under pressure to take more decisive action as the virus begins altering everyday life for nearly every American.
On Thursday, CNN reported that the President had decided to make the declaration but that it was undergoing legal review at the White House.
Washington Gov. Jay Inslee, a Democrat, spoke to Vice President Mike Pence on Thursday and requested that the Trump administration declare an emergency to provide vital assistance to states such as Inslee's that are on the front lines of the coronavirus crisis, a Washington state official told CNN.
The official told CNN they are "hopeful that (Friday's) announcement will provide the kinds of assistance that the governor requested."
White House aides have been weighing the move for the past several days as a way to provide more resources for combating the coronavirus outbreak. Trump has also been debating whether to support a legislative package to combat the outbreak negotiated by House Speaker Nancy Pelosi and his treasury secretary Steven Mnuchin.
Trump signaled in the Rose Garden that he does not currently support the House Democrats' coronavirus bill, which would -- among other things -- provide paid leave to Americans who can't go to work during the pandemic.
"We just don't think they're giving enough. We don't think the Democrats are giving enough," he said.
The emergency declaration would free up funding and allow the Federal Emergency Management Agency to head certain aspects of the outbreak response.
Earlier this week, Senate Minority Leader Chuck Schumer, in conjunction with Democratic Sens. Patty Murray of Washington state and Gary Peters of Michigan, sent a letter asking Trump to "immediately" consider disaster declaration requests for the coronavirus.