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Outbreak: The Virus That Shook The World, which airs this evening, charts the early stages of the virus and how it spread from the Hubei province capital.
The documentary features undercover footage of medical professionals who witnessed some of the first cases of the virus, which was filmed secretly by a citizen journalist.
In the footage, they say they were in no doubt about just how dangerous the virus was, but were forced to remain quiet about their concerns.
One medic, whose face is blurred, said: "We all felt there shouldn't be any doubt about human to human transmission."
In the clip, they also claim they had been aware of deaths as early as the end of December 2019.
Another medic noted: "Actually, at the end of December or beginning of January , the relative of someone I know died of this virus.
"Many of those living with him were also infected, including people I know."
Speaking after Wuhan was released from lockdown, the experts also detail a cover-up by the Chinese government authorities from the start of the outbreak.
One said: "We knew this virus transmitted from human to human. But when we attended a hospital meeting, we were told not to speak out.
"The provincial leaders told the hospitals not to tell the truth."
They argued that authorities knew new year celebrations in January would 'accelerate the speed of the virus', adding: "People suggested at city level that it shouldn't go ahead, but it did because such an event would present a harmonious and prosperous society."
The programme also features an interview with Dr Yin-Ching Chuang from the Infectious Diseases Prevention and Treatment Network in Taiwan, who fought to get himself and his team to Wuhan to work out whether there was human-to-human transmission - something Chinese authorities had denied.
Dr Chuang explained: "While we were at the meeting, we asked a lot of questions, very unwillingly they finally came out and said, 'Limited human-to-human transmission can't be ruled out'."
Two weeks after the outbreak had officially begun, the potential for human-to-human transmission was still not being publicly shared.
Dr Chuang continued: "What was the scale of infection? How big was this epidemic? How many patients were affected? We didn't know. Only they knew this."
"Why didn't China inform other countries of this human-to-human matter earlier?"
The documentary also unearths evidence showing that, while the virus was spreading between 5 January and 17 January, no new cases were officially reported in China during the 12-day period.
Infectious diseases specialist Dr Yi-Chun Lo, the Deputy Director-General of Centres for Disease Control in Taiwan, said: "The very early outbreak management was just a mess, a failure.
"I think the pandemic could have been avoided at the beginning if China was transparent about the outbreak and was quick to provide necessary information to the world."
According to ITV, the Chinese government has declined to comment, but previously said it had provided timely information once facts were known.
Watch Outbreak: The Virus That Shook The World on ITV at 9pm on Tuesday 19 January.
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