Four US airlines canceled dozens of flights to and from Mexico City's international airport on Thursday after the Popocatepetl volcano blew ash and steam skyward, officials said.

American Airlines, US Airways, Delta Airlines and Alaska Airlines "decided not to conduct operations to and from Mexico City," airport spokesman Jorge Andres Gomez told Milenio television.

A fifth US carrier, Spirit Airlines, canceled its flights to Fort Lauderdale, Florida, and Dallas, Texas, from the Toluca airport, 68 kilometers west of the capital.

Another spokesman for the Mexico City airport told AFP that the airlines canceled a total of 47 flights between Mexico and the United States.

The airlines took the precautionary measure even though the airport decided to keep its runways open.

"There is a very thin presence of ash, which does not harm operations or affect equipment. The decision is not questionable, it's within their right," the spokesman said.

Volcanic activity at the snow-capped Popocatepetl, located 65 kilometers (40 miles) southeast of the capital, has intensified since May, prompting authorities to raise the alert level to "yellow phase 3" for 27 days, just short of evacuation orders.

In its latest bulletin, the National Disaster Prevention Center said 12 hours of tremors were felt around the 5,452-meter (17,887-feet) volcano, which had spewed steam, gas and ash in the past 24 hours.