President Donald Trump is reportedly planning to declare a national emergency over the coronavirus pandemic in a move that would unlock billions of dollars of federal aid for states and localities.

Trump will do so by invoking a law known as the Stafford Act, according to reports. The act empowers the Federal Emergency Management Agency to coordinate a national response during "natural catastrophes" and to assist state and local governments. Invoking the act, which can only be done by the president, also unlocks FEMA's $40 billion disaster relief fund.

Bloomberg News was the first to report the development. The president will reportedly announce the declaration during a press conference at 3 p.m. Friday.

Declaring a national emergency would represent a significant turning point for the president. Trump has in the last few days mentioned that an emergency declaration was under consideration but has not publicly committed to invoking the measure. During remarks at the White House on Thursday, Trump said he was still considering what emergency action to take.

"We have very strong emergency powers under the Stafford Act," Trump said. "I have it memorized, practically, as to the powers in that act. And if we need to do something, I'll do it."

He did not commit to using the act, instead saying he may be working on "more minor" things, adding that the U.S. is "in great shape."

Democratic lawmakers have for days urged Trump to declare a national emergency. Three dozen Democratic senators on Wednesday sent a letter to Trump asking him to declare a national emergency under the Stafford Act in order to free up FEMA's disaster relief fund.

Photos: Washington State Confronts COVID-19 View All 11 Images

"Why he hasn't done it is a mystery," Senate Minority Leader Chuck Schumer of New York said in a speech on the Senate floor. "We need him to do it and do it now."

The Stafford Act would allow states to request a 75% federal cost-share for emergency expenses like medical supplies and equipment, vaccinations, temporary medical facilities and ambulances, according to the senators' letter.

Invoking the act for a public health crisis would not be unprecedented: President Bill Clinton in 2000 declared emergencies under the measure to address the West Nile Virus in New York and New Jersey.

Trump has also invoked the act for a number of natural disasters during his term, including in response to wildfires in California and major flooding in the Midwest.