The seven-year-old boy fell down the 20-metre-deep hole first, and his 41-year-old father jumped afterwards in a bid to save him.
The father managed to keep his son afloat until a team of specialist rescue firefighters arrived, 11 minutes after the alarm was raised, to extract them.
The child was rescued in nine minutes.
The incident happened on Sunday afternoon in the village of Vale da Figueira, in Mexilhoeira Grande.
The boy was pulled out with just cuts and bruises while the father was found to be suffering from hypothermia.