Wuhan, the original epicentre of the coronavirus, had hosted a mass banquet on the occasion of the Lunar New Year for tens of thousands of people, six days before the Chinese government made it public that a pandemic had broken out, AP reported on Wednesday. Chinese President Xi Jinping warned the public on January 20, the seventh day.

However, by that time over 3,000 people had been infected, the news agency said citing documents it acquired and estimates by experts based on retrospective data. China eventually shut down Wuhan on January 23.

“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.”

Apart from the six days when Chinese officials hid information about the deadly virus, its Center for Disease Control did not register any cases from local officials, despite hundreds of patients appearing in Wuhan’s hospitals and in other parts of the country from January 5 to January 17. It’s also uncertain whether local officials failed to report cases or national officials failed to record them.

But China’s censorship of information, its bureaucracy and reluctance to send bad news to top officials hindered the fight against the disease in its early phases, the report said. The Chinese government also punished eight doctors who had blown the whistle early, accusing them of “rumour mongering”.

“Doctors in Wuhan were afraid,” said Dali Yang, a professor of Chinese politics at the University of Chicago. “It was truly intimidation of an entire profession.”

It was only when the first case was reported in Thailand on January 13 that Chinese officials purportedly began to take action at home, including a nationwide plan to find cases, distribution of testing kits, easing the criteria to confirm cases and asking health officials to conduct screening. However, all this was done without the knowledge of the public until January 20.

China reopened Wuhan on April 8, after two-and-a-half months of draconian restrictions. On Wednesday, Chinese officials denied to AP that they had suppressed information. “Those accusing China of lacking transparency and openness are unfair,” Foreign Ministry Spokesperson Zhao Lijian said.

But AP said the documents show that the head of China’s National Health Commission, Ma Xiaowei, held a confidential teleconference with provincial health officials on January 14, in which he conveyed instructions from President Xi Jinping, Premier Li Keqiang and Vice Premier Sun Chunlan. However, the memorandum does not clarify what these instructions were.

“The epidemic situation is still severe and complex, the most severe challenge since SARS [Severe Acute Respiratory Syndrome] in 2003, and is likely to develop into a major public health event,” the memo said. “With the coming of the Spring Festival, many people will be traveling, and the risk of transmission and spread is high. All localities must prepare for and respond to a pandemic.”

However, in an official statement issued to AP, the National Health Commission, China’s top medical body, claimed China had published information on the outbreak in an “open, transparent, responsible and timely manner,” in accordance with “important instructions” repeatedly issued by Xi.

Over 20 lakh people around the world have been infected, and over 1,37,000 have died, according to an estimate by Johns Hopkins University. In China, over 82,000 people diagnosed positive for Covid-19, and over 3,300 died, according to official figures.