It is believed the woman was fishing at San Remo, near Phillip Island, on rocks near the George Bass Coastal Walk about 10.50am when she was washed into the water.
As of 6pm, the search is still ongoing.
Ambulance Victoria sent a helicopter to the area this morning.
Local police are being supported by the police Air Wing and Life Saving Victoria in searching for the woman.
Anyone who witnessed the incident or with information is urged to contact Crime Stoppers on 1800 333 000 or make a report at www.crimestoppersvic.com.au