Police and ambulance crews were called at about 15:25 BST on Tuesday.
Of the three people hurt, one was airlifted to hospital.
Two people had minor injuries and were also treated at hospital before they were discharged.
A Health and Safety Executive (HSE) spokesperson said: “HSE is aware of the incident and is assisting Devon and Cornwall Police with their inquiries.
“Our thoughts are with those affected by this incident and their families during this sad time.”