Cruise ship operator Norwegian has proposed resuming voyages from the US in July, with all crew and passengers 100 per cent vaccinated against Covid-19.

It has also improved facilities on-board its ships, including introducing "hospital grade" air filtration, contact tracing technology, upgraded intensive care units and quarantine medical facilities.

Norwegian Cruise Line Holdings Ltd, the parent company of Norwegian Cruise Line, Oceania Cruises and Regent Seven Seas Cruises, has written to the US Centres for Disease Control and Prevention requesting that its vessels be allowed to start operating from US ports from July 4.

Its ships are frequent callers to Bermuda and account for about 50 of the 127 cruise ship visits that were originally scheduled for the island this year.

In a letter to the CDC, Norwegian outlined its plan, which it said is consistent with the CDC's updated guidance and "exceeds the intent" of the CDC's conditional sail order released last week.

Frank Del Rio, Norwegian's chief executive officer, said: "Because our return to service plan mandates that the entire population on-board our vessels be vaccinated, our plan reduces the risk of outbreaks and severe Covid-19 cases.

"We have invested tens of millions of dollars in enhanced on-board health and safety protocols, including, but not limited to, enhanced hospital grade air filtration systems, cutting-edge contact tracing technology and significantly upgraded ICU and quarantine medical facilities.

"Our vessels are well equipped to handle the one-off case of infection that could occur, and our procedures are well detailed and resourced to treat, address and otherwise handle any isolated case on-board."

The company will require all passengers and crew to have proof of being fully vaccinated with an approved Covid-19 vaccination at least two weeks before going on-board one of its ships.

There will also be protocols for universal Covid-19 testing of crew and guests.

Norwegian proposes commencing sailings from US ports, initially with 60 per cent on-board capacity, increasing this by 20 per cent every 30 days.

It has requested the CDC lift the conditional sail order for all NCLH cruise vessels departing from US ports effective July 4.

The CDC's conditional sail order includes instructions to increase from weekly to daily reporting frequency of Covid-19 cases and illnesses and implementing routine testing of all crew, and establishing a plan and timeline for vaccination of crew and port personnel.

It said Covid-19 vaccination efforts would be critical in the safe resumption of passenger operations, and that the next phase of the order would include simulated voyages to allow crew and port personnel to practice new Covid-19 operational procedures with volunteers before sailing with passengers.