Norwegian Cruise Line has announced cancellations across nearly half of its fleet as the Omicron variant continues to punish the sector's upcoming bookings.

The Miami-based flagship subsidiary of Norwegian Cruise Line Holdings said the cancellations affect eight of its 17 vessels.

The cancellations stretch well into April, although some of the vessels return to service before then.

Norwegian blamed the growing restrictions associated with a spike in Covid-19 infections.

"Our first priority is the health and safety of our guests, crew and the communities we visit," it said.

"Due to ongoing travel restrictions, we've had to modify a few sailings and unfortunately have had to cancel voyages."

Health officials are warning against cruise travel, with Covid-19 infections reaching record levels.

On Sunday, the Brazilian Health Regulatory Agency called for a halt in cruises until 21 January. Cruise lines have indicated they will comply with the voluntary measures.

The US Centres for Disease Control has also increased the Covid-19 risk for cruise ships from level 3 to level 4, leading it to recommend avoiding cruise travel, regardless of vaccination status.

Last month, Norwegian's larger rivals, Carnival Corp and Royal Caribbean Group, acknowledged that the Omicron variant has led to an increase in cancellations and a fall in near-term bookings.

But they both gave bullish signals for booking volume and pricing for the second half of this year.