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New York City Mayor Bill de Blasio on Thursday said new data suggests that the first cases of the novel coronavirus may have surfaced in the city in late January -- weeks earlier than what was previously known.

De Blasio, during his daily press conference Thursday, was asked about a new report released by Columbia University which claims that had lockdown measures been put in place just one week earlier, fewer than 4,300 people would have died in the New York Metro area, compared to the 21,800 people that died by May 3.

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“I wish we had known so much more in January, February, the beginning of March,” de Blasio said. “I wish we had the testing that would have told us what was going on.”

“We’re not sure when this disease started to be present in the city,” de Blasio continued. “We thought it was March, and now, more and more, it’s looking like it was February or even late January and we just didn’t have the testing to be able to give us the full picture.”

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De Blasio added that it is “very painful” to reflect on, saying he wishes city officials “had known then the things we know now.”

In hindsight, the mayor may regret statements he and others in the administration made at the time.

On Jan. 24, de Blasio said New Yorkers should "continue living as you have"; on Feb. 14 he said, "this should not stop you from going about your life ... from going out to Chinatown and going out to eat"; and on March 13, he reiterated "we wanted people to go on about their lives."

In a March 2 tweet, de Blasio wrote: “Since I’m encouraging New Yorkers to go on with your lives + get out on the town despite Coronavirus, I thought I would offer some suggestions. Here’s the first: thru Thurs 3/5 go see 'The Traitor' @FilmLinc. If 'The Wire' was a true story + set in Italy, it would be this film.”

New York City Health Commissioner Oxiris Barbot remarked on Feb. 2: "There is no reason not to take the subway, not to take the bus, not to go out to your favorite restaurant, and certainly not to miss the parade next Sunday.”

On Thursday, De Blasio went on to note that March 1 was the first reported positive case of COVID-19 in New York City, and the first death was on March 14.

“We were fighting in those two weeks to see if we could contain this without any ability to see how deeply it spread, because we didn’t have the testing, and you know, immediately after that first death, it was the next day that I indicated and called for the schools to close,” de Blasio said, adding that he ordered restaurants and bars close as well. “And two days later, I called for shelter in place.”

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He added: “As we got information, we acted…But of course, it’s painful. And of course, now I look back and I wish we had known more because we would have been able to do more. It’s as simple as that."

New York, which has been considered the epicenter of the COVID-19 pandemic in the U.S., as of Thursday, reported more than 353,000 positive cases and more than 22,800 deaths.

In New York City alone, as of Thursday, there were more than 195,000 positive cases of the novel coronavirus and more than 15,780 deaths.

The Columbia University study revealed this week that if the United States had begun social distancing measures and lockdown measures just one week earlier than it did in March, nearly 54,000 fewer people would have died in the U.S. by early May.

As of Thursday, the U.S. has reported more than 1.5 million positive cases of COVID-19, and more than 93,500 deaths.

Meanwhile, last week, de Blasio said New York City won’t reopen before June “unless something miraculous happens."

“Unless something miraculous happens, we’re going into June,” de Blasio said Monday, adding that New York City is “clearly not ready yet.”

He added: “It’s fair to say by June we will make progress if we keep up what we have been doing.”

De Blasio said last week that the earliest non-essential businesses in the city could open is June 7.

Fox News' Gregg Re contributed to this report.