Frustrated passengers stood in long lines at Mexico City's airport Friday as US airlines canceled flights for a second day after the Popocatepetl volcano spewed a new column of ash.

United Airlines, Delta Airlines, Alaska Airlines and AirTran voluntarily scrapped 15 flights as a precaution, but the airport did not restrict travel as it did not consider the ash a risk, airport spokesman Jorge Andres Gomez told AFP.

On Thursday, six US airlines had canceled some 60 flights, stranding 600 passengers, with many of them still looking for a way out of the Mexican capital Friday afternoon.

"They can't even give us chairs," Mexican traveler Gabriela Garcia said as she stood in a long line at a Delta counter with some 200 other people. "Nobody knows anything, nobody says anything, we've been standing for six hours."

Another Mexican traveler, Eusebio Pacheco, said that he had also been waiting in line for six hours with his wife, hoping to finally take off to the Canadian province of Quebec.

"We don't know anything, they don't tell us anything, we're desperate," he said, adding that two flights were canceled. They hoped to fly out on Saturday.

A Slovenian couple who were heading to Paris with Delta said they were advised to book a hotel and return in two days, with the airline saying it wouldn't pay for food or lodging since it was a weather event.

The airport spokesman said operations were getting back to normal later in the day and that flights from Europe and other regions had been landing all day.

The National Disaster Prevention Center had reported early Friday the 5,452-meter (17,887-feet) high volcano had blown a 1.5 kilometer (one mile) high column of ash that was heading west-northwest and produced low-intensity tremors in the last 24 hours.

In an evening bulletin, the agency said the volcano had spewed more gas, steam and ash which had dispersed as it blew west. Authorities flew over the crater and saw molten rocks that were blown one kilometer into the air before falling on the mountain's slopes, it added.

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.

The disaster prevention center advised people living around the volcano to wear long sleeves and use masks or cover their mouths and noses with a cloth.