Six people were hospitalized, according to Italian news agency ANSA, mostly with head injuries in non-critical condition.
One volcanologist told Ms Morelle the explosion was the most most unsafe he had seen in his 30-year career. Eruptions occur frequently, although incidents that involve injured tourists are rare.
Mount Etna spewing lava Thursday, hours before the incident.
Morelle said that she encountered burning boulders, getting pelted by rocks and boiling steam.
The lava flow originated much higher on Mount Etna than where the tourists and film crew were, but it's the nature of a phreatic eruption that made it unsafe for the onlookers who were still significantly away from the eruption site.
Reports indicate that 10 people were injured, but everyone survived.
Tourists, journalists and scientists hoping for a better look at Europe's most-active volcano were in for a shock as it suddenly erupted on Thursday.
Sicily's volcano had been putting on a show in recent days, with a new lava flow starting from the south-eastern crater on Wednesday.
The volcano, one of the world's most active, last erupted two weeks ago on the Italian island.
Morelle said a big ash cloud was visible above Etna and the plume from the explosion was visible a long way off. Here's NewsCamerawoman with the massive hole a lump of rock burnt through her coat. pic.twitter.com/GVSyj3Sa9A- Rebecca Morelle (BBCMorelle) March 16, 2017 Ten people suffered injuries as a result of the eruption.