The first case is believed to be a 55-year-old man in Hubei province who was seen by doctors on November 17. Over the next month, one or two cases were seen a day, until the infection rate picked up in late December.

The local cluster of seemingly incurable pneumonia cases was reported to Chinese health bosses on December 27, when there were about 180 confirmed cases, and the World Health Organization was informed on December 31.

Dr Kanji says the official figures carried by popular trackers such as those run by Johns Hopkins University and Worldometer use China's official figures, which only begin on January 22, when there were 555 confirmed cases.

He modelled the spread of the disease based on a patient zero on December 1 - two weeks after the first case was detected.

"In my modelling, the minimum number of cases in China has to be 300,000 people," with a minimum 30,000 dead, he said.

"Lockdown didn't occur in China until January 23, so it's been going on for a few months all on its own."

Disputed mortality rate

And the mortality rate - estimated somewhere between 1 and 5 percent by most health agencies to date - is likely a lot higher, Dr Kanji said - especially when compared with the flu.

"The death rates in Italy are 42 percent of closed cases. In Spain it's 25 percent of closed cases. The flu kills around half a percent of people. This is not your regular flu. It's way more infectious and it's way more virulent."