THE U.S. Centers for Disease Control and Prevention (CDC) said people should avoid traveling on cruise ships regardless of their vaccination status, as daily COVID-19 cases in the country climb to record highs due to the fast-spreading Omicron variant.

The move delivers another blow to the cruise industry that had just started returning to the seas in June after a months-long suspension of voyages caused by the pandemic.

The CDC on Thursday raised its COVID-19 travel health notice level for cruise ships to its highest warning level, citing reports of COVID-19 outbreaks on cruises.

The health agency has investigated and still probing into COVID-19 cases on more than 90 ships. It starts scrutiny if 0.10% or more passengers on guest voyages test positive for COVID-19.

Shares in Carnival Corp, Norwegian Cruise Line Holdings Ltd and Royal Caribbean Group reversed course to fall about 1% after the travel advisory from the CDC.

"The decision by the CDC to raise the travel level for cruise is particularly perplexing considering that cases identified on cruise ships consistently make up a very slim minority of the total population onboard," the Cruise Lines International Association said.

Norwegian Cruise, meanwhile, said it believed guests on its ships were better protected from contracting COVID-19 than in any other general population setting.

The company and Carnival said the CDC's decision had not impacted scheduled itineraries.

The CDC said passengers already on cruise ships should get tested three to five days after their trip ends, and self-monitor for COVID-19 symptoms for 14 days.

The Omicron variant also continued to impact air travel. Total flight cancellations within, into, or out of the United States stood at more than 1,180, with over 10,300 flights delayed as of 14:37 ET, data from flight-tracking website FlightAware.com showed.