Nearly half of the city's young adults have no desire to raise a family, says the Family Planning Association.
In its latest Youth Sexuality Study, which is carried out in Hong Kong every five years, the association found that 45 per cent of male respondents and 39 per cent of females were either unsure, or had made a firm decision not to have children.
A total of 1,223 young Hong Kong people aged from 18 to 27 were interviewed between October and December last year.
For those who planned to marry and raise families, the ideal number of children, according to the survey, were 1.5 for female respondents and 1.4 for males.
'If the real birth rate turns out to be about 1.4 to 1.5, this will be barely enough to replace the city's ageing population,' said Professor Paul Yip Siu-fai, chairman of the association's research subcommittee.
According to the Census and Statistics Department, the number of live births per 1,000 females in the population were 1.13 in 2010 and 1.19 in 2011.
The latest government population-policy report issued in May says that the city's ageing population has accelerated, and that more than four in 10 Hongkongers would be too old to participate in the labour market within three years.
The professor, who has been advising the Central Policy Unit on the issue of the city's ageing population, said the real challenge in boosting local birth rates lay at the hesitation among young adults to get married, as giving birth out of wedlock was unusual among Hongkongers.
The survey found that 45 per cent of females respondents, and 49 per cent of males, were undecided about marriage. These figures are the highest among males, and second highest for females, in all the surveys conducted during the past two decades.
Yip said another study had found that 22 per cent of the city's women would never marry.
'If we want to see an increase in the birth rate, it's highly important for the government to encourage people to get married,' he said.
The professor suggested that the government take the lead to implement supportive family-friendly measures, such as reducing the length of working hours, so that young adults would have more leisure time to seek a suitable partner.
Yip said this suggestion was backed by the survey. Some 42 per cent of the women and 36 per cent of the men said they did not want to walk down the aisle because they could not find an ideal partner.
'Many Hongkongers don't want to get married because they can hardly afford a flat in the private market,' Yip said.
'I think the government should help them get rid of the roadblocks that are preventing them from getting married.'