Four US airlines have cancelled dozens of flights to and from Mexico City's international airport after the Popocatepetl volcano blew ash and steam skyward.

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.

Another spokesman told AFP that the airlines cancelled 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, 65 kilometres south-east 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 Centre said 12 hours of tremors were felt around the 5,452-metre volcano, which had spewed steam, gas and ash in the past 24 hours.

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AFP