A huge plume of ash, gas and rock spewed forth Monday from Italy’s Mount Etna, Europe’s largest active volcano, after a portion of its southeastern crater likely collapsed, authorities said.

Images showed a massive grey cloud billow forth from the volcano on the island of Sicily, beginning about 11:24am local time (0924 GMT), according to the National Institute of Geophysics and Volcanology (INGV).

Surveillance cameras showed “a pyroclastic flow probably produced by a collapse of material from the northern flank of the Southeast Crater”, the agency said.

A pyroclastic flow occurs when volcanic rock, ash and hot gasses surge from volcanos. They are extremely dangerous.

The explosive activity “had transitioned to a lava fountain”, INGV said, with the plume of ash expected to dissipate towards the southwest.

A red alert issued for aviation authorities said the height of the volcanic cloud was estimated at 6.5 kilometres.

The nearby Catania airport was still in operation.