A heavily pregnant woman was hospitalised after a man punched and stomped on her in a Sydney cafe last night in an apparent random attack.

About 10.30pm last night, a 31-year-old woman was with friends at a cafe on Church Street in the centre of Parramatta, in the city's west.

Police said a man approached her table and then viciously assaulted the woman who is 38 weeks pregnant.

"The man allegedly leaned over the table and punched the woman in the head multiple times before she fell to the ground where it's alleged the man stomped on her head," New South Wales Police said in a statement.

Other people at the cafe came to the woman's aid and managed to pull the man off her and hold him until police arrived.

The women said she didn't know the man.

A 43-year-old man was arrested and taken to Parramatta Police Station where he was charged with assault occasioning actual bodily harm and affray.

He was refused bail and will appear in Parramatta Local Court today.

The woman was treated at the scene before being taken to Westmead hospital for observation.