Hong Kong's population would drop nearly 10 per cent, to 6.2 million, within 30 years without the daily influx of migrants, according to projections by a statistician.
Paul Yip Siu-fai said that, according to the latest by-census figures, if the influx stopped the population would start shrinking from 2016, and would be falling by 0.8 per cent a year by 2036.
The ratio of dependent people, such as children and the elderly, would increase from 360 per 1,000 adults to nearly 650 by 2036.
The ratio of females to males - currently more than one to one - would also decrease.
Dr Yip, of the University of Hong Kong, a member of the Sustainable Development Council subcommittee drafting the city's first consultation paper on population policy - said people should not be too alarmed by the figures but a serious debate was needed on immigration policies.
'Of course there will be migrants coming to Hong Kong. This projection tells us their importance to this city. We rely on new arrivals a lot more than other migrant countries, such as Australia or Canada.
'Just look at these figures. We know for sure the existing scheme for mainland students studying and talent working here should be expanded. We also need a lot of babies.