Mothers and children were moved to different wards in the building, the hospital’s chief executive said.
Other patients have been contacted to have their elective operations and appointments rescheduled.
Father-to-be Damian Vanner told BBC News his pregnant partner had already been induced when she had to be evacuated from the maternity ward.
He said: “After speaking with staff and overhearing rushed working contractors, the conclusion appears to be that an over-spill of sewerage has come into contact with an electrical distribution board for a large section of the hospital.”
The hospital has not confirmed the cause of the flooding. Lancashire Fire and Rescue Service have been assisting the hospital in clearing standing water in the unit.
Due to the severe flooding, the hospital has reduced visiting times for friends and families on the wards, but stressed that it did not include patients who were terminally ill or receiving end-of-life care.
Chief executive Trish Armstrong-Child said the hospital’s urgent care pathway is also “under a lot of pressure” and urged people to think before attending its A&E.
She said: “Overnight, the basement of the women and children’s unit at Blackpool Victoria Hospital experienced severe flooding. This has led to a loss of power and network access to the entire building.
“We have received support from Lancashire Fire and Rescue Service to reduce the localised flooding, but further work is required today to clear the area of standing water.
“Due to this incident, we have contacted patients to rearrange their elective surgery where necessary. If you haven’t been contacted, please attend your appointment as planned.
“Outpatient activity due to take place in the women’s and children’s unit is being individually risk-assessed and where appropriate diverted. We have contacted patients to cancel or rearrange their appointments as necessary. If you haven’t been contacted, please attend your appointment as normal.
“Please be assured that all patients within the hospital are safe and continue to receive appropriate care.
“The hospital’s urgent care pathway is also currently under a lot of pressure. We are appealing to our communities to think before attending our Emergency Department and to use NHS 111 for advice and guidance.”
She added: “Colleagues from across the executive and senior leadership teams are working closely together and with our partners in the wider care community to ensure the trust remains focused on this important work and I’d like to thank everyone for their ongoing efforts.”