The Centers for Disease Control and Prevention is telling Americans to avoid all nonessential travel to China, expanding its travel warning from the city of Wuhan to the entire country as the coronavirus outbreak worsens, the agency said Tuesday.

Last week, the CDC advised against all nonessential travel to Wuhan, the epicenter of the disease's outbreak and where the majority of cases have been reported.

The U.S. Department of State on Monday also raised its travel advisory for China from Level 2 to Level 3, asking Americans to "reconsider travel to China due to the novel coronavirus." They added that some areas have "added risk."

Chinese health authorities said Tuesday that the virus, which was first diagnosed less than a month ago, has now killed 106 people and infected 4,515.

Scott Gottlieb, a former Food and Drug Administration Commissioner and a CNBC contributor, said he's worried that coronavirus cases in China are actually much higher than the official numbers show.

"I think we are dramatically underestimating" cases in China by "tens of thousands," Gottlieb told CNBC's "Squawk Box."