Police search for Sydney good Samaritan

A man who stopped to help a woman who was seriously injured when she was pushed onto a busy road in north Sydney may have the key to solving the cowardly crime.

The 54-year-old woman was standing at a bus stop in Lane Cove when a man pushed her in the back about midday on August 30.

The fall left her with a fractured elbow and fractured pelvis, police say.

The good Samaritan, who is believed to be a tradie driving a white ute, provided first aid to the woman but left before police arrived on the scene.

Officers are now seeking the man, believing he may have "vital information" that could help them identify the woman's attacker.