Emergency officials said eight others were injured in the collapse, with two people suffering serious injuries.
Five helicopters and dozens of emergency workers have been sent to the scene to assist with rescue efforts.
Video of the incident showed an ice mass collapsing down the slopes of Marmolada, the area's highest mountain.
"Unfortunately, five people were found lifeless," emergency services spokeswoman Michela Canova told the AFP news agency, adding that the injured figure "remains a provisional count."
"An avalanche of snow, ice and rock which in its path hit the access road when there were several roped parties, some of which were swept away," Ms Canova explained. "The definitive number of mountaineers involved is not yet known," she added.