Victoria Police said the woman fell into the water near theGeorge Bass Coastal Walk in San Remo about 10.50am on Thursday after being swept off rocks.
Officers spent most of the day combing the area with the assistance of the police air wing and Life Saving Victoria but as of 9.30pm on Thursday,the woman was yet to be found.
A police spokeswoman said crews would meet in the morning to reassess the operation.
Victoria Police urged anyone who witnessed the incident or with information to contact Crime Stoppers on 1800 333 000,while Life Saving Victoria reminded Victorians to be safe in the water.
With revellers expected to flock to pools and beaches to cope with the weekend’s forecast hot weather,water authorities are warning against taking alcohol and drugs near the water.
Drownings are twice more likely to occur on a public holiday or a long weekend,particularly if alcohol and drugs are consumed.
Police officers will be dispatched to key boat ramps across the state to test Victorians for both substances,which played a role in 31 per cent of drownings in the state over the past decade.