US airlines have cancelled dozens of flights into Mexico City over fears that volcanic ash from a rumbling volcano would affect their planes.
Delta and American were among the airlines cancelling more than 40 flights into the capital on Thursday.
Popocatepetl volcano has been rumbling all year, and began spewing ash and steam earlier in the week.
Airport authorities have kept the runway open and say the volcano poses no risk to flights.
"There is a very thin presence of ash, which does not harm operations or affect equipment," an unnamed airport spokesman told AFP news agency.