Victoria Police say they hold grave concerns for the welfare of a woman who has been missing since last Wednesday morning.

Police say Sandra Pevitt, 45, was last seen as she left her Werribee home in Melbourne's south-west, after she told family members she was going to the doctor.

However, calls to her regular doctor revealed that she did not have an appointment.

Ms Pevitt is described as 167 centimetres tall with shoulder-length blonde hair and frameless glasses.

Her car, a silver station wagon, is also missing.

Those with information on Ms Pevitt's whereabouts are encouraged to contact police.

Police are also concerned about another woman, Katie Dircks, 30, of Elwood, who has not been seen since Friday.