Scientists from Italy’s National Institute of Geophysics and Volcanology (INGV) in Catania said the activity centred on a lava flow on the mountain’s southeast slope.
Ash from the eruption blanketed roads, balconies and roofs of nearby towns, according to Italy’s civil protection agency, but there were no immediate reports of injuries or property damage.
Earlier on Monday, authorities issued a warning for aircraft in the area.
The nearby Vincenzo Bellini international airport in Catania closed at lunchtime until further notice, with inbound flights diverted to Palermo.
At 3324 metres, Etna is the tallest active volcano in Europe and has erupted frequently in the past 500,000 years.
Its volcanic activity has been well-documented throughout history.
Perhaps its most-devastating eruption occurred in 1669, when lava buried dozens of villages and proceeded to cover large sections of Catania, the biggest city in the eastern part of the island.
Earlier this month, a particularly powerful eruption spewed geysers of lava rocketing forth into the night sky over Sicily and the mountain has remained highly active ever since.
INGV scientists have recorded a gradual uptick in seismic tremors caused by escaping gases, which they say could be an indication that Etna is heading toward another spectacular burst of fiery lava fountaining, or paroxysmal volcanic activity.
They believe the eruption was caused by an accumulation of magma, noting that the same situation occurred about a year ago, albeit with more magma buildup.
By October, Etna had erupted another 50 times.
