NSW man allegedly stabbed father

A man has suffered critical injuries after he was allegedly stabbed by his son in Sydney's southwest.

The man believed to be in his 50s was found with a number of stab wounds at a house in Punchbowl just after 11am on Tuesday, police say.

The man's son, believed to be in his 30s, has been taken to Bankstown Police Station for questioning.

The father has been taken to Liverpool Hospital with critical injuries.