The U.S. Department of State on Sunday advised U.S. citizens against traveling by cruise ship as cases of the novel coronavirus continue to spread across the world.

"U.S. citizens, particularly travelers with underlying health conditions, should not travel by cruise ship," the State Department wrote in its warning.

The warning comes with new guidance from the Centers for Disease Control and Prevention that includes tips for people who do choose to travel by cruise ship. The U.S. has 554 confirmed cases of the coronavirus with 21 deaths as early Monday.

"Like many other viruses, COVID-19 appears to spread more easily between people in close quarters aboard ships," the CDC wrote.

See latest rules, waivers:Cruise lines adapt travel restrictions as coronavirus spreads

The CDC reports those with underlying health issues and older travel should avoid cruise ships altogether, along with long airplane trips and crowded places. Tips from the CDC while aboard a cruise ship, which the government entity said should be "especially" avoided, include:

Avoid contact with sick people.

Avoid touching your eyes, nose, or mouth with unwashed hands.

Clean your hands often by washing them with soap and water for at least 20 seconds or using an alcohol-based hand sanitizer that contains 60%–95% alcohol. Soap and water should be used if hands are visibly dirty. It is especially important to clean hands after going to the bathroom; before eating; and after coughing, sneezing or blowing your nose.

Avoid traveling if you are sick.

If you get sick with fever or new or worsening cough or difficulty breathing during your cruise, stay in your cabin and notify the onboard medical center immediately.

"Person-to-person spread of COVID-19 is occurring and countries are reporting both travel-related cases and community spread of the disease," the CDC wrote. "As the outbreak of COVID-19 continues, there remains a risk of infected travelers and crew boarding cruise ships."

Cruise ship will dock:Grand Princess cruise ship hit by coronavirus will dock Monday in California

For those who have been on a cruise ship within the last two weeks, the CDC recommends monitoring your health for 14 days after returning to the U.S., staying home if you're feeling sick and limiting your interactions with others, washing your hands and seeking medical advice.

Call and discuss recent travel and symptoms before going an emergency room or doctor's office, according to the CDC.

There are more than 110,000 confirmed cases of the coronavirus worldwide.

"In order to curb the spread of COVID-19, many countries have implemented strict screening procedures that have denied port entry rights to ships and prevented passengers from disembarking," the State Department wrote.

"In some cases, local authorities have permitted disembarkation but subjected passengers to local quarantine procedures."