Sen. Richard Burr, R-N.C., is facing calls to resign after reports Thursday that the powerful Intelligence Committee chairman had privately warned well-connected donors of the dire impacts of the coronavirus pandemic last month while selling off up to $1.6 million of his own stocks.

ProPublica reported that Burr — who co-wrote an op-ed for Fox News in early February saying "the United States today is better prepared than ever before to face emerging public health threats, like the coronavirus" — unloaded the stock around mid-February, about a week before the market started to plunge because of coronavirus concerns.

That included selling off up to $150,000 worth of shares of Wyndham Hotels and Resorts, which has lost two-thirds of its value, ProPublica reported. He also dumped to $100,000 of shares of another hotel chain, Extended Stay America.

ProPublica discovered, and NBC News has confirmed, the stock sell-offs in Burr's publicly available financial disclosure reports. The exact figures are unclear because the reports offer ranges of transactions.

The Senate Intelligence Committee received a number of briefings and intelligence reports in January and February that included non-public information about the growing coronavirus pandemic, Senate aides have told NBC News. The intelligence remains classified — it's unclear what warnings were given and exactly when.

Rep. Alexandria Ocasio-Cortez said on Twitter that as chairman of the Intelligence Committee, Burr "got private briefings about Coronavirus weeks ago. Burr knew how bad it would be. He told the truth to his wealthy donors, while assuring the public that we were fine. THEN he sold off $1.6 million in stock before the fall. He needs to resign."

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The stock market has declined about 30 percent since Burr dumped the shares.

A spokesperson for Burr said the sales were "personal transactions made several weeks before the U.S. and financial markets showed signs of volatility due to the growing coronavirus outbreak."

"As the situation continues to evolve daily, he has been deeply concerned by the steep and sudden toll this pandemic is taking on our economy," the spokesperson said.

Disclosure records also show that three other senators sold major holdings around the same time, including Sens. Dianne Feinstein, D-Calif., Kelly Loeffler, R-Ga., and James Inhofe, R-Okla., according to The New York Times.

In two tweets Thursday night, Loeffler, whose husband is the chairman of the New York Stock Exchange, defended the stock sales and said the investment decisions are made without knowledge of her and her husband.

She said in a follow-up tweet, "As confirmed in the periodic transaction report to Senate Ethics, I was informed of these purchases and sales on 02/16/2020 — three weeks after they were made."

Meanwhile, a Feinstein spokesman told NBC News Friday: "Senator Feinstein did not sell any stock. The transactions you're referencing were made by her spouse. All of Senator Feinstein's assets are in a blind trust, as they have been since she came to the Senate. She has no involvement in any of her husband's financial decisions."

Rep. Joaquin Castro, D-Texas, said Burr's selling off the stocks should be investigated.

"As a member of the House Intelligence Committee, I know that our committee receives sensitive information, including assessments and projections, before others in Congress and the general public (if ever). Senator Burr should suspend his chairmanship pending investigation," Castro tweeted.

Earlier Thursday, NPR reported that Burr had delivered a stark warning on the likely fallout of the virus at a luncheon with donors and well-connected constituents on Feb. 27.

"There's one thing that I can tell you about this: It is much more aggressive in its transmission than anything that we have seen in recent history," Burr said, according to a recording of the remarks obtained by NPR. "It is probably more akin to the 1918 pandemic."

He also warned: "Every company should be cognizant of the fact that you may have to alter your travel. You may have to look at your employees and judge whether the trip they're making to Europe is essential or whether it can be done on videoconference. Why risk it?"

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Burr's office confirmed his attendance at the event and the authenticity of the recording to NBC News, but it disputed the characterization of the event.

Burr pushed back on Twitter, as well, saying the lunch was hosted "by the North Carolina State Society. It was publicly advertised and widely attended. NPR knew, but did not report, that attendees also included many non-members, bipartisan congressional staff, and representatives from the governor's office."

"Every state has a state society. They aren't 'secretive' or 'high-dollar donor' organizations. They're great civic institutions that bring people in D.C. together for events, receptions, and lunches. And they're open to anyone who wants to get involved," Burr tweeted.

NPR reported that it had obtained a copy of the RSVP list for the event and that it included dozens of invited guests representing companies and organizations from North Carolina. The companies or their political committees donated more than $100,000 to Burr's election campaign in 2015 and 2016, NPR reported. NBC News has not seen the RSVP list and cannot confirm that independently.

Burr's office said his comments at the luncheon were in line with other comments he's made publicly encouraging the government to use every tool at its disposal to fight the virus.

"Senator Burr has been banging the drum about the importance of public health preparedness for more than 20 years. His message has always been, and continues to be, that we must be prepared to protect American lives in the event of a pandemic or bio-attack," spokesperson Caitlin Carroll said.

"Every American should take this threat seriously and should follow the latest guidelines from the CDC and state officials," she added.

On the same day Burr was speaking at the luncheon, President Donald Trump was telling reporters that the coronavirus is "going to disappear."

"It could get worse before it gets better. It could maybe go away. We'll see what happens," Trump said.