Airport officials say at least six US airlines have cancelled more than 40 flights into and out of Mexico City and Toluca airports after the Popocatepetl volcano spewed out ash, steam and glowing rocks.
Mexico City airport spokesman Jorge Gomez said US Airways, Delta, United, American and Alaska Airlines cancelled 47 flights as a precaution.
But he said the airport otherwise continues to operate normally and that by Thursday afternoon (US time) no ash had reached the area, about 70 kilometres from the volcano.
Gomez said some of the cities affected by the cancellations are Houston, Dallas, Denver, Phoenix, Chicago and Los Angeles.
At nearby Toluca airport, Spirit Airlines cancelled flights from Dallas and Fort Lauderdale. Toluca airport spokesman Alejandro Munoz says the airport also continues to operate normally.
"The decision not to fly from Mexico City has been made by these airlines, but the airport is in operable conditions," Andres Gomez, another airport representative, said on local television.
Mexico's leading airline AeroMexico suspended flights briefly, but resumed operations less than an hour later.
The volcano Popocatepetl in the central state of Puebla has been more active this year, prompting officials to raise warning levels but have so far ordered no evacuations.
Officials have kept the volcano's risk level on hold at "yellow," the second highest on the four-color spectrum, indicating that there is more activity than usual but no threat of eruption, national emergency services coordinator Luis Felipe said on Twitter.
On Thursday, ash fell on communities adjacent to the volcano, nicknamed Don Goyo, and reached southern neighbourhoods of Mexico City.
There is no evidence of volcanic ash in the airport's immediate vicinity, it announced through its Twitter account.
Volcanic ash can damage jet engines.
Authorities registered several tremors at the 17,886-foot (5,450-metre) volcano, which has been spraying a fountain of hot rock and ash for the last 24 hours.
An iconic backdrop to Mexico City's skyline on clear days, Popocatepetl sits roughly halfway between Mexico City and the city of Puebla.
Mexico City's airport serves more than 29 million people a year and oversaw 174,511 takeoffs and landings between January and June.
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