A woman is fighting for life after she was allegedly shot multiple times in the head with a nail gun in Sydney's west on Christmas Day.

The woman's son has since been charged over the domestic-related incident.

Emergency services were called to a home on Messina Crescent in Bonnyrigg Heights about 10.30pm to reports of an injured woman.

Police were told the 50-year-old woman became involved in an altercation with her 20-year-old son, before she was allegedly shot in the head a number of times with nails from a nail gun. Her son allegedly fled.