AP: MEXICO CITY (AP) — At least six U.S. airlines canceled more than 40 flights into and out of Mexico City and Toluca airports Thursday after the Popocatepetl volcano spewed out ash, steam and glowing rocks, airport officials said. Mexico City airport spokesman Jorge Gomez said U.S. Airways, Delta, United, American and Alaska Airlines canceled 47 flights as a precaution. But he said the airport otherwise continues to operate normally and that by Thursday afternoon no ash had reached the area, about 40 miles (70 kilometers) 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 canceled flights from Dallas and Fort Lauderdale, said spokesman Alejandro Munoz. The airport, about 35 miles (60 kilometers) from Mexico City, also continued to operate normally, Munoz said. Authorities registered several tremors Thursday at the 17,886-foot (5,450-meter) 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.