It’s believed three men were diving for shell fish near rocks off Fingal Beach when they got into trouble about 8am.
A 50-year-old Keysborough man managed to get to shore and raise the alarm.
A 42-year-old St Albans man and a 34-year-old Vermont South man are still missing.
Water Police are being assisted by Air Wing, SES, Parks Victoria, Lifesaving Victoria, Ambulance Victoria and local marine volunteer groups.
Anyone with any information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential crime report at www.crimestoppersvic.com.au