The coronavirus outbreak in the U.S. could grow to be as serious as it is in Wuhan, China, Johns Hopkins University Dr. Marty Makary told CNBC on Tuesday.

"What happened in Wuhan could happen here. Why do we think otherwise?" Makary said on "Squawk Box," referencing the Chinese city where the new virus originated in December.

The city of 11 million people was locked down on an unprecedented scale as the outbreak intensified. It remains on lockdown even as new cases in the region decline.

New cases in Wuhan and its surrounding Hubei province have dropped to below 50 a day, according to figures from the Chinese government, even as the disease spreads at greater rates across the globe.

"The American immune system is not stronger than the Chinese immune system," said Makary, a surgeon and professor of health policy and management. "Viruses don't care about politics and they don't care about location."

Worldwide, there are more than 114,000 confirmed coronavirus cases and more than 4,000 deaths, according to data from Johns Hopkins. There are cases in more than 100 countries and regions. But China has the most by far.

Outside of China, Italy is home to the most COVID-19 cases, with at least 9,172 confirmed cases and more than 450 deaths.

Italy on Monday extended its travel restrictions to include the entire country of 60 million people. They should not travel other than for work or emergencies, Prime Minister Giuseppe Conte said.

There are now more than 750 confirmed cases in the U.S., with 26 deaths.

"We need to tell people right now to stop all nonessential travel. I feel strongly about that," Makary said, adding he does not "like the idea of talking about contingency plans, but we've got to start making these plans."

"We've got to brace for a three-month problem," said Makary, author of-

Makary urged that the U.S. should take the disease more seriously, saying he's was worried about the capacity of the nation's health-care system to handle a serious spike in cases.

America has about 100,000 intensive care unit beds that "operate at full capacity or near full capacity," he said. "If we get 200,000 critical care cases, we're going to be overrun," he warned. "So we need to do more."