Chalit Thipkham, chief of Hang Dong district, said the accident happened at 7.30am at the resort in Ban Chang Kham Luang village in Tambon Ban Waen.
The injured were public health volunteers from Tambon Ban Ton Pao Hospital in Chiang Mai’s San Khampaeng district.
Chalit said 45 public health volunteers, all women, from the tambon hospital were having a retreat at the resort and after they attended a session at the meeting room of the resort, almost all of them came out to pose for photos on the balcony.
Ten others suffered minor injuries and were discharged after received treatment at the Hang Dong Hospital.
The district chief said the resort building was built lawfully in line with the approved blueprint but the balcony was added later without seeking permission.