Cruise ships won't be hitting the high seas again anytime soon.

The Centers for Disease Control and Prevention extended a "no sail order" Thursday that it imposed last month to help quell the spread of the coronavirus.

While the March 14 order was intended as a voluntary measure to stay in place for 30 days, the new one could last longer. 

The CDC order states that cruise ships can't board passengers and return to their sailing schedules until one of three events takes place:

• Expiration of the Department of Health and Human Services' declaration that COVID-19 constitutes a public health emergency.

•The CDC director's own decision to modify or rescind its no-sail decision.

•Passage of 100 days from the time the new order is published in the Federal Register.

Until then, the about 100 cruise ships in the Atlantic, Pacific or Gulf of Mexico must remain idle, either in port or wallowing at anchor, the CDC said. Those ships currently have nearly 80,000 crew aboard.

“The measures we are taking today to stop the spread of COVID-19 are necessary to protect Americans, and we will continue to provide critical public health guidance to the industry to limit the impacts of COVID-19," said CDC Director Robert Redfield in a statement. 

Cruise ship lines have already voluntarily suspended most operations, leaving a dwindling number of ships left at sea with passengers aboard. Many have struggled to find ports that will allow their passengers to disembark. One ship still in operation is Princess Cruises' Pacific Princess, en route to Hawaii and then to Los Angeles with 115 passengers aboard after cutting short a westbound around-the-world cruise in Australia. The only passengers left aboard are those who had medical issues that prevented them from flying home.

Cruise ships, with their confined environments, have been hit particularly hard by the coronavirus pandemic. The CDC notes that in recent weeks, crew members or passengers have developed either flu-like symptoms or tested positive for COVID-19 on at least 10 cruise ships.

On some of the vessels, passengers or crew members died either on the ship or after being moved ashore to hospitals.

The Cruise Lines International Association didn't immediately offer a statement on the extension of the CDC order. But upon the March 14 order, CLIA Global Chairman Adam Goldstein said it was understood to be necessary.

“We do not take this decision lightly, and we want the traveling public to know in no uncertain terms the commitment of this industry to putting people first,” he said.