A third person, who was able to free himself, suffered minor injuries and is being treated in hospital.
The three were working to broaden an alpine path between Ruosalp and Alplen near Unterschachen in the canton of Uri at an altitude of about 1,500m when the rockslide happened at around 3pm, said Uri police.
Rescue workers attended the scene by Rega helicopter.
The site remains unstable and geologists are assessing the situation.
The incident is the latest in a spate of rockslides to hit the Swiss Alps in recent months.
One of the country's largest ever swept through the Val Bregaglia in August, leaving eight hikers missing, presumed dead, and villages cut off and uninhabitable.