The US has barred all passengerships from sailing within its territories until perhaps mid-July, handing the reeling sector yet another challenge amid the coronavirus pandemic.

The US Centers for Disease Control and Prevention (CDC) has extended a no-sail order for such vessels for the next 100 days following numerous onboard outbreaks.

Carnival Corp, Royal Caribbean Cruises, Norwegian Cruise Line Holdings and other cruiseship owners have already suspended their fleets for weeks — and, in some cases, to June.

"We are aware of the CDC order and are studying how best to respond to its provisions," Royal Caribbean spokesman Jonothan Fishman told TradeWinds.

Calls to Carnival and Norwegian were not immediately returned.

Shares for the "Big Three" cruise behemoths made gains during Friday's morning trading on Wall Street amid news that they can survive the mass layups for many months.

Carnival stock gained 3.6% to $12.42, while Royal Caribbean's shares went up 7.1% to $40.22 and Norwegian's shares rose 1.9% to $13.11.

The CDC said it is working with the cruise line industry to address the health and safety of crew at sea and communities surrounding points of entry for US cruiseships.

“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 on its workforce throughout the remainder of this pandemic," CDC director Robert Redfield said in a statement.

The order ceases cruiseship operation in waters in which the US may exert jurisdiction and requires forming an operational plan approved by CDC and the US Coast Guard (USCG) to address the pandemic.

US territories include American Samoa, Guam, the Northern Mariana Islands, Puerto Rico and the US Virgin Islands.

Measures may include monitoring and screening passengers and training crew to handle an outbreak.

Cruiseship operators may not embark and disembark passengers or crew at ports or stations, except as directed by the USCG and other authorities.

There are about 100 cruiseships at sea off US East, West and Gulf coasts, with nearly 80,000 crew onboard, according to the CDC.

The CDC is also aware of 20 cruiseships at port or anchorage in the US with known or suspected Covid-19 infection among onboard crew.

The CDC said it may lift the suspension within 100 days if Covid-19 is no longer considered a public health threat.

Celestyal Cruises, an operator in the eastern Mediterranean, announced on Friday that it had extended the suspension of operations to 29 June as a result of Covid-19. It originally planned to resume business on 1 May.