Police officers have called off the search in Belfast Lough which began yesterday evening after a report that a baby had gone into the water with a woman who was later rescued.
A police spokesperson said: "Following an extensive search operation involving several agencies and volunteers and after enquiries with the 37 year old woman and her family, police now understand the report of a baby going into the water was incorrect. We do not believe there was a baby in the woman's care on the ferry."
Earlier, the Coastguard stated that there was no chance of the baby being found alive.
Announcing that the search would be turned over to police, Coastguard watch officer Jude McNeice said: "We've got no chance of finding the child alive after 18 hours, so we will be handing over to the police for the recovery phase."
Police and Coastguard helicopters took part in last night's search. Four lifeboats and a police boat were involved.
Eyewitnesses had said the child was with a woman who plunged from the Stena Line boat as it made its way into Belfast port from Cairnryan on Scotland's western coast.
The sea search for the infant restarted this morning in poor weather conditions.
The woman was rescued and taken to the Royal Victoria Hospital in Belfast for treatment, where she is stable. She was recovered by a pilot boat 15 minutes after the alarm was raised.
The incident happened in Belfast Lough, close to Holywood, Co Down, at around 6.10pm on a busy shipping route for passengers and freight between Northern Ireland and Scotland.
John McPoland, a spokesman for the Northern Ireland Ambulance Service, said two ambulance crews treated her.
"She had been in the water for a while so you can understand that with the coldness of the water she would have been hypothermic," he said.
Coastguards received a call from the ferry reporting that two people were in the water in Belfast Lough. One person was recovered by the pilot boat at 6.25pm, 15 minutes after the alarm was raised and taken to hospital.
Bangor and Donaghadee RNLI lifeboat, an Irish Rescue helicopter, police helicopter, fast rescue craft from two ferries, tugs and a pilot boat are all engaged in today's search in the vicinity of Victoria Channel.
Coastguard rescue teams from Bangor and Portmuck were also searching the shoreline of Belfast Lough.
A PSNI spokesman confirmed the missing person was believed to be a young child.
Agencies, including the police helicopter, the Irish Coastguard and the RNLI have been involved in the search for the baby.
Police Service of Northern Ireland officers boarded the ferry, which is docked in Belfast Port.
A PSNI spokesman said: "It was reported that two people fell into the water from a ferry. One person was rescued and was taken to hospital for treatment for suspected hypothermia."
All Stena Line sailings to and from Belfast were cancelled last night and Belfast Port was closed.