More than 160 flights out of Chicago’s two international airports were canceled on Tuesday morning because of heavy fog, disrupting plans for Christmas Eve travelers.

O’Hare International Airport reported 91 canceled flights as of 1:30 p.m. local time, with average delays of more than half an hour, and Midway International Airport reported 71 cancellations.

A ground stop for arriving flights into Chicago was in effect from about 5:30 a.m. until 9:30 a.m., said Lynn Lunsford, a spokesman for the F.A.A.

The agency said on Twitter, “Passengers flying through @fly2ohare and @fly2midway should contact their airline regarding delays due to fog.”