MEXICO CITY, May 21 (Xinhua) -- Mexican authorities on Sunday raised the alert level due to the recent increased activity of Popocatepetl volcano.

The alert level was raised from yellow phase two to yellow phase three, one step below the red alert, said Laura Velazquez, head of the Mexican National Civil Protection Coordination Agency, at a press conference.

The yellow phase three alert signals "intermediate to high" volcanic activity such as persistent plumes of smoke, gas and light ashfall, along with explosions of increasing intensity with the launch of incandescent rocks.

The Scientific Advisory Committee, which is made up of various experts, recommended raising the alert level due to increased volcanic activity since Friday, said Velazquez.

Popocatepetl has registered more frequent exhalations and even moderate explosions accompanied by the expulsion of ash and incandescent rocks.

Ashfall from exhalations and explosions forced the closure of Mexico City's two main airports for several hours on Saturday.

The volcano, standing over 5,400 meters above sea level, is situated about 70 km southeast of Mexico City, between the central states of Puebla, Morelos and the State of Mexico.