The flood of pregnant mainlanders gatecrashing emergency wards doubled last year - and at least 700 have been rejected at the border in the past three months.
The new rush spells double trouble for overburdened hospitals.
Secretary for Food and Health York Chow Yat-ngok said that Hospital Authority figures show 1,656 non-local expectant mothers flocked to emergency wards without reservations last year - twice the 796 of 2010.
And last month 203 pregnant mainlanders rushed to accident and emergency departments compared with just 88 in December 2010.
The Immigration Department revealed yesterday it rejected at least 700 pregnant mainlanders at border points from October to December in an indication of tougher measures.
To better monitor the situation, the department has opened 13 new e-channels at Lo Wu control point and eight more at the Lok Ma Chau control point for mainland visitors since Tuesday.
A spokesman said more e-channels would improve customs checks on mainlanders, especially those who are pregnant.
"We will inquire if these females have prior bookings of hospital beds and delivery packages," said the spokesman.
"Doctors from the Department of Health will also work at the Lo Wu control point to screen these 'alleged' heavily pregnant women and measure the number of their pregnancy weeks."
A spokesman for the Hospital Authority said: "It is dangerous for heavily pregnant women to be rushing to emergency wards at the last minute for delivery. Both the mother and baby are taking high risks."
He said facilities and equipment in these wards are different from standard obstetrics wards, and have insufficient manpower.
The absence of antenatal records for such mainlanders affects the decision and direction of medical treatment undertaken in emergencies.
Chow admitted the alarming figures posed problems but refused to comment further, quoting Chief Executive Donald Tsang Yam-kuen as saying the relevant bureau will communicate with mainland authorities on how to tackle the problem of mainland women giving birth here.
"In terms of the capacity of the maternity services, so far we are able to cope with the requirement that it is for both mainland as well as local mothers.
"Of course, the priority is always given to local mothers and we do not set any quota for local mothers at all," Chow added.
He said by March he would discuss with private hospitals the quota of mainland women to give birth in Hong Kong,
"This year's quota of 35,000 is at an acceptable level in terms of the capacity of maternity services,' he said.
But if there is any necessary adjustment of quota next year, that will be subject to further discussions," he said.
The authority urged pregnant mainlanders to make appropriate delivery arrangements in the interests of safety, as service capacity will be filled by booked cases in public hospitals, leaving little room for non-booked cases.