Nobody was reported injured in the eruption, but the ash forced Catania-Vincenzo Bellini Airport, Sicily's busiest and Italy's sixth busiest airport, to close, canceling or delaying domestic flights, authorities said.
The eruption followed several earthquakes over several days that peaked at 7 p.m. local time Wednesday, the Agenzia Giornalistica Italia news agency reported.
By 9 p.m. Etna erupted and lava started flowing, the agency said.
The 11,000-foot-high mountain, Europe's largest active volcano, had its last major eruption in 1992.
Etna's March 11, 1669, eruption was its most violent, killing 15,000 people. Lava flows that day destroyed villages at Etna's base and submerged part of Catania.