Ecuador declared a national alert after the Tungurahua volcano, notorious for previous eruptions, began spewing lava again, forcing closure of schools and a widening evacuation of residents.

There were no immediate reports of casualties from the latest eruption.

A 5-mile-high column of lava and ash generated a vast, stifling canopy of poisonous gases and smoke, forcing the authorities to issue repeated warnings over radio and television to fleeing residents of four towns to cover against the contaminated air.

The National Secretary of Risk Management in Ecuador, Maria del Pilar Cornejo, said three of the affected towns had been evacuated.

The towns of Cusua, Bilbao and Chacabuco were among those worst affected by the volcano's eruptions.

Residents were ill-equipped for the burst of lava and gas as the volcano erupted after several explosions Monday. The air was thick with lava ash around the mountain, in the Cordillera Oriental region of central Ecuador's Andean region south of Quito.

Damage to agricultural crops and livestock could be extensive, officials said.

Numerous residents were treated for breathing problems and lava injuries but there were no immediate reports of fatalities, though rescue teams remained cautious in their assessments of the damage and the lava's toll on humans and livestock.

Officials said authorities in towns near the volcanic eruption responded by shutting down schools, businesses closed and streets were deserted before the evacuations began.

News media said more communities might be evacuated. The numbers of those displaced were not immediately available.

The state-run Geophysical Institute said lava flowed from the crater, at a height of more than 16,480 feet, down the slopes and into mountain settlements and villages.

The institute recorded at least six explosions inside the crater before the eruptions began. It said the first activity began April 20 but officials had no immediate word on whether they took action in response to the renewed activity.

Tungurahua is 16,479 feet above sea level, and is about 80 miles southeast of Quito. It has been active since 1999, when volcanic activity restarted.

Tungurahua, "Throat of Fire" in the indigenous Quichua language, was dormant for many years but became active in 1999, losing its ice cap. Major eruptions on Aug. 16, 2006; Feb. 6, 2008; May 28, 2010; and Dec. 4, 2010, caused havoc and killed at least four people.

Numerous residents reported severe health problems after each eruption.

Before the volcanic activity began in 1999 Tungurahua used to be snow-covered and bore a summit glacier that melted away.