Sydney woman attacked with hammer

A woman has serious head injuries after being attacked with a hammer in Sydney's west in what's believed to be a domestic assault.

Police have arrested a 54-year-old man after the woman, also aged 54, was assaulted at a home in Cecil Hills on Monday.

She's been taken to Liverpool Hospital, while the man has been taken to Green Valley Police Station for questioning.

* National domestic violence helpline: 1800 737 732 or 1800RESPECT. In an emergency call triple-zero.