Millions in Mexico warned to prepare for evacuation as Popocatépetl volcano spews ash

Millions of people in Mexico have been warned to prepare for a possible evacuation after increased activity from the country's most dangerous active volcano, which has been spewing ash into several nearby towns since last week, according to authorities.

Some 25 million people live in a 60-mile radius of the volcano, which is about 45 miles southeast of Mexico City and located between the states of Morelos, Puebla and state of Mexico.

On Sunday, the National Civil Protection Coordination (CNPC) increased its volcanic threat level to "yellow phase 3," which calls on some 3 million people who live in towns and villages adjacent to the volcano to stay alert and prepare for a possible evacuation.

The CNPC also warned of greater volcanic activity and the dispersion of ash into several nearby towns at high speed. It also recommended that residents nearby avoid outdoor activities.

"In the case of Mexico City, the risk is ash fall. We are prepared for that scenario and we know what to do. Let's stay alert," Mexico city's mayor Claudia Sheinbaum said in a tweet on Sunday.

"Air travelers may continue to experience additional flight delays, cancellations, or temporary airport closures with little or no warning," the US embassy in Mexico said, with the airport also issuing a similar alert.

State authorities have also suspended in-person classes in schools across 40 municipalities in Puebla, five municipalities in the state of Mexico and seven in Tlaxcala and said the classes will be held remotely.

The embassy also recommended people to not travel within a 7.5 mile radius of the volcano, citing warnings from local authorities.

The volcano had been dormant for decades until it erupted in 1994. Since then, its rumblings have become a part of daily life for residents.