(Reuters) -Shares of U.S. airlines and other travel-related companies fell on Monday as rising Omicron cases and weather-related problems forced the cancellation of hundreds more flights, leaving travelers stranded across the country during the holidays.

Over 800 flights were canceled within, into, or out of the United States on Monday, data from flight-tracking website FlightAware.com showed.

That was on top of over 3,000 flight cancellations during the Christmas holiday weekend, typically a peak time for travel for Americans.

Shares of American Airlines (NASDAQ:AAL) Group Inc, United Airlines Holdings (NASDAQ:UAL) Inc, Delta Air Lines Inc (NYSE:DAL) and Southwest Airlines (NYSE:LUV) Co were down between 2% and 3% in early trade.

Most airline stocks have rallied this year on hopes of a travel boom as travelers start visiting friends and family after dealing with pandemic-related restrictions last year.

However, staff shortages at airlines, weather-related disruptions and now the fast-spreading Omicron variant have disrupted flights frequently this year.

Poor weather in some areas has also added to travelers woes.

Southwest Airlines said it had canceled about 50 of the 3,600 flights scheduled Monday due to weather-related problems. Delta, United, and American did not immediately respond to Reuters' requests for comment.

Separately, the Shanghai government said on Monday that the country's aviation regulator would suspend two China Eastern Airlines (NYSE:CEA) Corp Ltd flights from New York to Shanghai from Jan. 3 due to rising COVID-19 cases.

Other travel stocks also came under pressure as Omicron triggers fears of tougher restrictions.

Shares of Norwegian Cruise Line (NYSE:NCLH) Holdings, Royal Caribbean (NYSE:RCL) Cruises Ltd and Carnival (NYSE:CUK) Corp were down between 1.3% and 2.4%.

At least three cruise ships were forced to return to port over the weekend after COVID-19 cases were detected on board, according to media reports.

Travel firms Booking Holdings (NASDAQ:BKNG) Inc, Airbnb Inc, Expedia (NASDAQ:EXPE) Group Inc and Tripadvisor Inc were all down between 0.6% and 1.8%.

Hotel operators Marriott International (NASDAQ:MAR) Inc, Hilton Worldwide Holdings (NYSE:HLT) Inc and Hyatt Hotels (NYSE:H) Corp fell between 1% and 2%.