U.S. lab operator Quest Diagnostics said on Thursday it was launching a test service for coronavirus, a day after the Trump administration met with private lab test developers to discuss increasing the availability of diagnostics.

Quest said it would be in position to receive specimens for testing and begin to provide testing next week.

Wall Street plunged on Thursday, with the Dow Jones Industrial Average falling by 750 points the morning after a 1,200-point rally.

Traders continued to digest the economic impact of the coronavirus, after the number of confirmed U.S. cases mounted overnight.

Within minutes of the opening bell, every single component on the 30-member Dow index was down. The S&P 500 and the Nasdaq were both trading lower by just over 2 percent.

It's day four of a wild week for markets, with the Dow posting its second-biggest points gain on Wednesday after key wins by former Vice President Joe Biden on Super Tuesday.

Two more people in New York have tested positive for the new coronavirus, according to NYC Mayor Bill de Blasio, bringing the total across the state so far to 13.

Speaking on MSNBC's "Morning Joe" on Thursday, de Blasio said the patients were a man in his 40s and a woman in her 80s.

Gov. Andrew Cuomo confirmed the existence of 11 cases in the state on Wednesday, including the wife, son, daughter and neighbor of a Manhattan lawyer, who is being treated in a hospital.

Also in New York, two school districts in Westchester County have shut down schools until Monday after two students from the same family and a parent from a separate family were possibly exposed to the virus. Mount Vernon has shut 16 schools, while Hastings-on-Hudson has shut all three of its schools.

Both school boards stressed there were no confirmed cases among staff, students or parents and that the closures were to enable a deep clean under an "abundance of caution."

The two students who may have been exposed to the virus will be off school for two weeks.

HOUSTON — Dr. Peter Hotez says he made the pitch to anyone who would listen. After years of research, his team of scientists in Texas had helped develop a vaccine to protect against a deadly strain of coronavirus. Now they needed money to begin testing it in humans.

But this was 2016. More than a decade had passed since the viral disease known as severe acute respiratory syndrome, or SARS, had spread through China, killing more than 770 people. That disease, an earlier coronavirus similar to the one now sweeping the globe, was a distant memory by the time Hotez and his team sought funding to test whether their vaccine would work in humans.

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President Donald Trump confessed Wednesday that for the last few weeks he's been missing something: touching his face.

"I haven't touched my face in weeks,” Trump said during a meeting about coronavirus with airline executives. "I miss it."

He's not alone. The emergence of a new coronavirus around the world has triggered widespread warnings about personal hygiene and habits in an effort to limit its spread: wash your hands, limit unnecessary travel and don't touch your face.

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Japanese Prime Minister Shinzo Abe said on Thursday that visitors from China and South Korea — two countries hardest hit by the outbreak so far — would need to complete a two-week quarantine at a government facility, and would be barred from public transport

Japan has so far confirmed more than 300 cases and at least seven people have died, according to WHO data.

Meanwhile, Japan's Olympics minister signaled the Tokyo Olympics would go ahead as planned even as the outbreak spread to new parts of the country, with the western Shiga prefecture confirming its first case on Thursday. 

Japan also said Chinese leader Xi Jinping's state visit planned in April has been postponed.