Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

WASHINGTON — Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, recommended Sunday that elderly and vulnerable Americans limit their exposure to travel and large crowds as the world fights the coronavirus outbreak.

In an interview on NBC's "Meet the Press," Fauci said the elderly and those with "underlying conditions" are "overwhelmingly" more likely to have complications if they catch the coronavirus.

"If you are an elderly person with an underlying condition, if you get infected, the risk of getting into trouble is considerable. So it's our responsibility to protect the vulnerable," he said.

"When I say 'protect,' I mean right now. Not wait until things get worse. Say no large crowds, no long trips. And above all, don't get on a cruise ship."

"This will be a recommendation," Fauci said. "If you're a person with an underlying condition and you are particularly an elderly person with an underlying condition, you need to think twice about getting on a plane, on a long trip. And not only think twice. Just don't get on a cruise ship."

Full coverage of the coronavirus outbreak

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

He added that the nation may have to reconsider its approach to large social gatherings if the situation gets worse.

"They call it social distancing, but it's commonsense stuff. You don't want to go to a massive gathering, particularly if you're a vulnerable individual," he said.

"If we continue to see the community spread go up, I think you need to seriously look at anything that's a large gathering."

As of Saturday, there were 446 confirmed cases of coronavirus in the U.S. based on NBC News reporting, with more than half of states reporting at least one case.

There are more than 100,000 confirmed cases around the world, according to the World Health Organization. Some countries are taking dramatic steps in hope of stopping the virus' spread; in Italy, millions are on lockdown in the Lombardy region.

Federal and local governments and health agencies are scrambling to understand the virus' spread in the U.S. and take measures to stop it.

Gov. Larry Hogan, R-Md., said on "Meet the Press": "The governors are really on the front lines. I think there's been pretty good cooperation at the federal, state and local level, but this thing is escalating so rapidly that information is changing, not only on a daily basis, but almost on an hourly basis."

Download the NBC News app for full coverage of the coronavirus outbreak

Fauci admitted that early attempts to send out coronavirus tests were frustrated by delays, but he said the nation's testing capacity is "accelerating dramatically."

"Early on, there were some missteps with regard to the test and some technical aspects to it. But right now, I believe, 1.1 million tests have already been sent out. By Monday, there'll be an additional 400,000. And by the end of next week, probably around 4 million," he said.

Even so, he added that while "we're getting a better sense" of the scope of the outbreak "as the days go by," "unfortunately that better sense is not encouraging, because we're seeing community spread," which is when the virus spreads locally instead of only to people with exposure abroad.