Travelers at Mexico City’s airport on Friday had to withstand lines that stretched far outside the hub’s doors and onto the sidewalk just to drop off their bags as airlines were hit with staffing shortages due to Covid-19.

At least 65 Mexico City flights were canceled over the past 24 hours, according to tracking site FlightAware. Over the past week, 71 Aeromexico pilots have tested positive for Covid, as have four Aeromar pilots, according to Captain Jose Suarez, spokesperson at pilot union ASPA, which represents 1,900 pilots at Grupo Aeromexico SAB and Grupo Aeromar SA.

Around 4% of VivaAerobus SA’s crew is currently in isolation because of a suspected or confirmed infection, the company said in response to questions.

Mexico registered 25,821 new Covid-19 cases on Thursday, the most since August, as the omicron variant spreads through the country. Deaths and hospitalizations have remained low when compared to past waves. The country has fully vaccinated 57% of its population.

“We’re seeing a domino effect,” said Suarez in a phone interview. “Every pilot that’s infected means their whole crew needs to be isolated.”

Aeromexico is “putting in place contact tracing protocols for various collaborators, including flight crews, which has resulted in adjusting planned operations,” the company said in a statement.

A spokesperson for Volaris said the airline didn’t know of infections among its crew or employees and that flights were operating normally. Aeromar didn’t reply to a request for comment.

Social media users complained of flights that had been delayed by more than 10 hours with little information from airlines. Videos showed crowded gates and hours-long delays to drop off bags.

In the U.S., Friday marked the fifth day this month with more than 2,000 scrubbed flights, as a jump in virus infections made it difficult for airlines to keep operations fully staffed and a winter storm blanketed the Northeast.