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The Dow Jones Industrial Average tumbled, soared, and then closed with a gain of 1,900 points after President Donald Trump declared a national emergency on Friday.

The Dow, which had surged by around 1,200 points earlier in the day, sank by around 500 points as the president began his address from the White House Rose Garden, flanked by health officials and members of the coronavirus task force.

The blue-chip index then rallied as key details of the White House response to the viral outbreak were revealed, with the S&P 500 notching up a gain of over 6 percent and the Nasdaq spiking by 5.5 percent.

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Trump also announced he was implementing a series of "decisive" measures to address the coronavirus pandemic, including a close collaboration with companies such as Walmart, Target, CVS, and Google.

Markets are still waiting for concrete action on an economic relief package, which lawmakers and the White House have so far failed to produce.

“I think we’re very close to getting this done. The president is absolutely committed that this will be an entire government effort, that we will be working with the House and Senate," Treasury Secretary Steven Mnuchin told CNBC Friday morning.

House Speaker Nancy Pelosi, D-Calif., vowed Friday to pass a coronavirus relief bill before the weekend, though she said negotiations with Mnuchin were still ongoing.

Market optimism also grew after news reports the Group of Seven governments would work together to create a coordinated economic response to the viral pandemic.

Friday's rally follows a massive meltdown, with Thursday marking the official end of the longest bull-market run in history. The S&P 500 plummeted 9.5 percent and the Dow tumbled by 10 percent.

It has been the worst week for equities since 2008, prompting questions as to whether or not the Federal Reserve will implement a massive rate cut of one full percentage point at its meeting next week.

“There are no guarantees here, and things could get worse,” Brad McMillan, chief investment officer for Commonwealth Financial Network, told CNBC. “If the number of cases continues to increase, the economic damage will go from hitting confidence to something worse. If the economy deteriorates, markets will reflect that shift."