Australian immigration minister Scott Morrison said one asylum seeker had died from head injuries as he was been taken by ambulance to the hospital. Two other seriously injured asylum seekers - one with a gunshot wound and the other with a fractured skull - are to be flown to Australia for medical treatment.
In recent years, thousands of people seeking asylum in Australia have attempted to reach the country by boat, mostly from Indonesia.
The government has intercepted them at sea and sent them to detention camps at Manus Island, part of Papua New Guinea, or the tiny Pacific atoll nation of Nauru.
Mr Morrison said the injuries had occurred outside the camp on Manus Island, which houses more than 1000 inmates.