Dr. Mehmet Oz said Monday on "Fox & Friends" that thousands of additional coronavirus cases will soon be confirmed in China and expressed alarm about the incubation period being specified by Chinese officials.

China on Monday expanded sweeping efforts to contain a viral disease by extending the Lunar New Year holiday to keep the public at home and avoid spreading infection as the death toll rose to 80.

Hong Kong announced it would bar entry to visitors from Wuhan, the mainland province at the center of the outbreak, following a warning the virus’ ability to spread was increasing. Travel agencies were ordered to cancel group tours nationwide, adding to the rising economic cost.

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Increasingly drastic anti-disease efforts began with the Jan. 22 suspension of airplane, train and bus links to Wuhan, a city of 11 million people in central China. That lockdown has expanded to a total of 17 cities with more than 50 million people.

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Oz said it's "concerning" to hear that 80 deaths have been confirmed, and there are "definitely" thousands of more cases yet to be confirmed. He said the youngest and oldest are being most affected, which is typical for such a viral outbreak.

"It's also alarming, this is the big news today, the Chinese leadership is starting to say 'this incubation period is a lot longer than we thought,'" he said, adding that it appears that someone who catches the new coronavirus can be contagious for weeks before even realizing they're sick.

"That would change the infectious nature of this. It does seem like once you've got the virus, you do seem to infect more people than usual," he added.

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In a viral video Monday, a Chinese nurse in Wuhan insisted the outbreak is far worse than officials have acknowledged.

“At this moment, [in the] Hubei province, including the Wuhan area ... even China, 90,000 people have been infected by a coronavirus," she stated.

The Associated Press contributed to this report.