Immigration officers say they have detected 23 mainland women suspected to have undergone sham marriages with Hong Kong men so that they could have babies in the city after the "zero-birth quota" policy came into effect on January 1.
They were tracked down in checks on private hospitals after suspicions were raised last month about some women who said their babies belonged to mainland men, not their Hong Kong husbands, and others who had apparently married after they fell pregnant.
One of the women is now serving a jail term, meaning her baby is likely to be born in Hong Kong anyway.
The policy, barring mainland women without Hong Kong husbands from giving birth in the city, was announced by Chief Executive Leung Chun-ying in April as part of efforts to stem a surge of such births by women seeking Hong Kong abode rights for their children.
"I hope these 23 cases were the last batch of such cases and no more mainlanders will try such a way to come to Hong Kong," the director of immigration, Eric Chan Kwok-ki, said yesterday.
He said some cases were discovered when the mother went to the department to register their births.
"The mother claimed to us the baby did not belong to her Hong Kong husband, but to a mainland man. So we found it suspicious."
Couples living on either side of the border with no record of visits to explain the pregnancy also provided clues, he said.
The first case to come to light was a 28-year-old pregnant woman who was stopped at the border in December and admitted under questioning that her baby's natural father was her ex-husband on the mainland, not her Hong Kong husband.
She was jailed for a year on February 1 for false representation and deception. That means the baby, if born in prison, will qualify for right of abode.
The department is investigating whether any agency was involved in helping the women find false husbands.
Last year the department inspected 61,831 pregnant mainland women and denied entry to 4,202 because they did not have appointments for obstetric services in hospitals in Hong Kong.
The department prosecuted 359 pregnant mainland women for breaching conditions of stay, and four agencies for helping them.