Norwegian Cruise Line, the world's third-largest cruise operator, raised doubts about its ability to keep running as a business, the first in the sector to signal it may succumb to the coronavirus crisis.

The company's shares slumped about 20% as it also launched a $US1.6 billion offering of shares and bonds in a scramble to raise money, and announced a $US400 million investment in a subsidiary from a private equity firm.

Norwegian Cruise and rivals Carnival Corp and Royal Caribbean Cruises have been among the most high-profile victims of the pandemic after deadly outbreaks on some cruise ships led to extended port quarantines in Japan and California.

Norwegian, which has suspended its sailings through June 30, has not yet announced a relaunch date.

The cruise industry was left out of a $US2.3 trillion US stimulus package for troubled companies as the major players are all incorporated outside the United States.

"COVID-19 has had, and is expected to continue to have, a significant impact on our financial condition and operations, which adversely affects our ability to obtain acceptable financing," Norwegian said, also flagging substantial doubt about its ability to continue as a "going concern".