In the six days after top Chinese officials secretly determined they likely were facing a pandemic from a new coronavirus, the city of Wuhan at the epicenter of the disease hosted a mass banquet for tens of thousands of people; millions began traveling through for Lunar New Year celebrations.

President Xi Jinping warned the public on the seventh day, Jan. 20. But by that time, more than 3,000 people had been infected during almost a week of public silence, according to internal documents obtained by The Associated Press and expert estimates based on retrospective infection data.

Six days.

That delay from Jan. 14 to Jan. 20 was neither the first mistake made by Chinese officials at all levels in confronting the outbreak, nor the longest lag, as governments around the world have dragged their feet for weeks and even months in addressing the virus.

But the delay by the first country to face the new coronavirus came at a critical time — the beginning of the outbreak. China’s attempt to walk a line between alerting the public and avoiding panic set the stage for a pandemic that has infected more than 2 million people and taken more than 133,000 lives.

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“This is tremendous,” said Zuo-Feng Zhang, an epidemiologist at the University of California, Los Angeles. “If they took action six days earlier, there would have been much fewer patients and medical facilities would have been sufficient. We might have avoided the collapse of Wuhan’s medical system.”

Other experts noted that the Chinese government may have waited on warning the public to stave off hysteria, and that it did act quickly in private during that time.

But the six-day delay by China’s leaders in Beijing came on top of almost two weeks during which the national Center for Disease Control did not register any cases from local officials, internal bulletins obtained by the AP confirm. Yet during that time, from Jan. 5 to Jan. 17, hundreds of patients were appearing in hospitals not just in Wuhan but across the country.

Read more: AP