INGV reports that lava was pouring from three vents during the night. The start of the eruption was preceded by a sudden increase in volcanic tremor amplitude at 18:00 UTC (20:00 CET) on April 13 and a short explosive activity at the new SE cone shortly after 20:00 UTC.
The lava flows appeared around 20:27 UTC, probably first from the summit vent, but were immediately followed by the opening and stronger lava effusion from the vent at the southern base of the crater complex, Volcano Discovery said. "It seems that shortly after that, a third effusive vent opened about half way between the other two vents on the upper slope of the SE crater complex, also feeding a lava flow."
Two of the lava flows stopped during the night, but the one from the lower vent continued traveling east and reached Valle del Bove slope at around 02:00 UTC. As of 12:41 UTC on April 14, the vent was still active.

Geological summary

Mount Etna, towering above Catania, Sicily's second largest city, has one of the world's longest documented records of historical volcanism, dating back to 1500 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km horseshoe-shaped caldera open to the east.
Two styles of eruptive activity typically occur at Etna. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more of the three prominent summit craters, the Central Crater, NE Crater, and SE Crater (the latter formed in 1978). Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend to the foot of the volcano on all sides and have reached the sea over a broad area on the SE flank. (GVP)

Featured image: New effusive eruptive phase begins at Mount Etna, April 13, 2017. Credit: Boris Behncke