The Centers for Disease Control and Prevention (CDC) has confirmed five cases of the new coronavirus in the US and health officials are now investigating 73 possible cases in 26 states.
Still, officials say there's no evidence that the deadly virus is spreading in the US and they categorize the risk to Americans as low.
Chinese authorities say the virus has killed more than 80 people in China and infected 2,750 people.
But public health experts in Hong Kong are warning that the numbers are significantly higher.
Dr. Gabriel Leung, the dean of medicine at the University of Hong Kong, suggests there could be as many as 26,000 people infected with the virus and that as many as 44,000 people could be incubating it.
He encouraged authorities on Monday to step up precautionary measures and warned that quarantines and travel bans implemented already may have not limited the spread of the virus.
The coronavirus causes cold and flu-like symptoms including cough and fever and sometimes shortness of breath and pneumonia.
Authorities in the US have hospitalized and isolated the five patients with it.
In China, 50 million people are already affected by travel bans.
The US consulate in Wuhan now plans to use a charter plane to evacuate Americans trapped in the region.
Authorities in Wuhan are racing to complete two new hospitals to house thousands of patients infected by the virus.
Workers are using pre-fabricated buildings and hope to complete the hospitals by next week.