Former FDA Commissioner Scott Gottlieb on Tuesday said he's worried that coronavirus cases in China are actually much higher than the official numbers.

"I think we are dramatically underestimating" cases in China by "tens of thousands," Gottlieb told CNBC's "Squawk Box." "I think the Chinese haven't been fully sharing."

Chinese officials on Tuesday sharply increased their confirmed coronavirus cases to nearly 4,700. The death toll in China rose to 106. The virus was first discovered in the city of Wuhan in Hubei province in December.

Gottlieb — a physician, health advocate and Pfizer board member — said it's hard to tell the total number of people who were infected in China since health officials there did not widely roll out diagnostic testing until late January.

"We know the numerator," said Gottlieb, who left the Food and Drug Administration in April 2019. "We don't know the denominator." Last week, he said there could be thousands of mild cases that will likely go undiagnosed and clear up on their own.

Later on "Squawk Box," House Energy and Commerce Chairman Frank Pallone said he's also skeptical of China's coronavirus reporting. "They are not often forthcoming; often don't tell the truth about what's really happening," said the New Jersey Democratic congressman.

China, accused of withholding information in the 2003 SARS epidemic, said its handling of the coronavirus will be different. Last week, the ruling Communist Party's central political and legal affairs commission warned, "Whoever deliberately delays and conceals reports will forever be nailed to history's pillar of shame."

Multiple coronavirus cases have been confirmed in Hong Kong, Macao, Taipei, Thailand, Vietnam, South Korea, Singapore, Malaysia, Japan, Australia, France and the United States.

Gottlieb, who is also a CNBC contributor, said on Tuesday that he expects the U.S., which confirmed five cases, to have smaller, "inevitable" outbreaks. However, he added that the U.S. can better contain the virus with preventative measures because its population is less dense than that of China.

U.S. health officials warned that the flu or other respiratory illnesses could complicate identifying more cases. They recommend that people call a health-care provider before seeking treatment so the appropriate measures can be put in place.