The World Health Organization said on Tuesday that a report that COVID-19 had appeared in France in December, earlier than previously thought "was not surprising", and urged countries to investigate other initial suspected cases.
The disease later identified as COVID-19 was first reported by the Chinese authorities to WHO on December 31 and was not believed to have spread to Europe until January.
"This gives a whole new view of everything," said WHO spokesman Christian Lindmeier in an interview with the UN in Geneva, referring to the French reports.
"The findings help to better understand the potential virus circulation of COVID-19."
Other possible previous cases may arise after re-testing the samples, he said.
A French hospital that retested old samples from patients with pneumonia found that it was treating a man who had COVID-19 as early as December 27, almost a month before the French government confirmed its first cases.
Lindmeier encouraged other countries to check case reports of pneumonia of unspecified origin in late 2019, saying it would give the world a "new and clearer picture" of the outbreak.
Asked about the origins of the virus in China, Lindmeier emphasized that it was "very, very important" to explore this.
US Secretary of State Mike Pompeo claims that his country has evidence that the new coronavirus has emerged from a laboratory in Wuhan, China, although scientists have warned the WHO that it is of animal origin.
"This may need more missions or a mission (for China), so we are looking forward to it," said Lindmeier.
WHO chief emergency expert Mike Ryan said on Monday that the WHO's chief raised the question of the virus's origins "at the highest level" during a WHO mission in China in January.