MILAN — Volcanic rocks and steam injured at least 10 people, including tourists and a scientist, following an explosion on Sicily's Mount Etna on Thursday, witnesses and media reported.

The tourists, who were drawn to Etna to observe the spectacle of the active volcano erupting, were caught by surprise when flowing magma hit thick snow, causing an explosion that rained rock and other material down upon them.

Authorities say about 35 tourists were on the volcano when the explosion occurred around midday, and that the guides who accompanied them helped bring them to safety.

The president of the Italian Alpine Club chapter in Catania, Umberto Marino, was traveling up the volcano in a snowcat when injured people started running in his direction.

"The material thrown into the air fell back down, striking the heads and bodies of people who were closest," Marino was quoted by the Catania Today website as saying.

According to Italian news agency ANSA, four people including three German tourists were hospitalized, mostly with head injuries. None of the injuries was listed as grave.

Among those present when the explosion occurred was a scientist from Italy's volcanology institute, Boris Behncke, who said on his Facebook page that he had suffered a bruise to his head. He added: "I am generally fine and having a good, well-deserved beer in this moment."

The BBC's global science reporter, Rebecca Morelle, was on assignment on Etna and described the experience in a series of tweets.

"Running down a mountain pelted by rocks, dodging burning boulders and boiling steam - not an experience I ever ever want to repeat," she wrote.

The BBC crew was shaken, but physically OK, having suffered cuts, bruises and burns, she wrote.

Morelle said the explosion was "a reminder of how dangerous (and) unpredictable volcanoes can be."

The tourists were in an area they were permitted to enter when the explosion occurred. Mount Etna has been active for the past two days, creating a visual spectacle as it spews lava and ash into the air. A new lava flow started from the southeastern crater on Wednesday, and was advancing with a temperature above 1000 degrees Centigrade (1,832 degrees Fahrenheit) in an area covered by snow.

Officials at Catania airport on Thursday announced it would reduce arrivals by half to five flights an hour due to ash clouds. Departures will continue as scheduled.

Italy's volcanology institute said it was continuing to monitor the phenomenon.