Taking care of an ageing group of mentally disabled people wasn't an issue in the past. The life expectancy for a person with Down's syndrome was just 26 in 1970. With improved therapy and facilities, many of the estimated 87,000 Hongkongers with mental disabilities now survive into their 60s and outlive their parents.

Increased life expectancy puts added demands on their carers as ailments associated with ageing, such as dementia and incontinence, start to surface after the age of 40. (Nearly half the people registered with the Hong Chi Association, the largest local NGO providing services for the intellectually disabled, are over 40.)

Anxious parents are exploring a variety of options to provide for their disabled children after they die.

Chung and her husband got a twentysomething niece to agree to care for Hang-chi after they die or grow too feeble, but she knows this is no guarantee for his future care. 'She's still so young. Maybe she'll get married or move away. Her next family might not accept my son,' says the retired import worker.

Although shy with strangers, Hang-chi is sociable and chatty once he's comfortable with someone. Chung says: 'My greatest hope is still that he can enter a hostel.'

Many elderly parents in a similar situation are keen to secure a place for their adult children in a hostel, where they can be cared for the rest of their lives. Such hostels, which are subsidised by the government, provide beds, meals, medication and 24-hour supervision.

But there's a wait of up to seven years (4,000 people are in the queue for one of 5,000 hostel places to become available; some of these facilities are woefully understaffed and others are overcrowded).

Priority to public hostels is given to people with the most severe disabilities, whose parents are either in nursing homes or deceased.

'The government assumes that the family will help, but none of us can rely on siblings or other relatives nowadays,' says Eva Mok Wai-ying, vice-chairman of the Hong Kong Joint Council of Parents of the Mentally Handicapped.

'They might be willing to provide monetary support, but what these children need most is constant surveillance.'

Mok speaks from experience. Her 27-year-old son, Yuk-ming, 'is a two-year-old in a man's body', she says. For years, the weight of caring for Yuk-ming fell on Mok; she was the one in her family of four who tended to his needs.

'My husband accepts him, but the care-giving was generally from me,' Mok says. At first her younger son could not comprehend his brother's behaviour, but he understood as he grew older.

Fortunately, Yuk-ming was accepted by a hostel when he turned 16.

'I can have my own interests now,' Mok says. 'Of course, I still worry about [what will happen to] him when I go, but at least now I know he has someone looking after him for the rest of his life.'

Responding to a greying community of mentally disabled, the government is decentralising its support, creating 16 district centres where parents can make appointments with social workers, physiotherapists and occupational therapists. The aim of these centres is to equip the mentally disabled with enough life skills to function independently.

'This is a step in the right direction,' says Dr John Lian Ming-gon, founder of the Centre for Advancement in Special Education at the University of Hong Kong. 'It gives families more face time with professionals. But of course, there are not enough of them.'

Last year the government also added 777 new places at day, residential and vocational centres for the mentally disabled - double the number for 2007-08.

To many parents and academics, this is far from adequate.

'There definitely needs to be more hostels,' says Dr Mark Li Kin-yi, a senior lecturer in social work at Baptist University. 'Obviously, if you have more people lining up for these facilities, you need more spaces.'

However, John Budge, a senior solicitor who takes on pro bono work involving the mentally disabled, says the answer isn't simply to expand services.

'It's like a bottomless pit. You can never get enough care,' says Budge, who has served on the boards of NGOs such as Hong Chi and St James' Settlement. 'We started [in 1965] with a special needs school that was just a choir room in a church and now we have an annual budget of around HK$500 million [earmarked for services for the mentally disabled].'

This is the combined allocation from the Social Welfare Department and the Education and Health bureaus, but critics say services will be more effective if there is greater collaboration between departments.

'There's a big difference between resources given to different bureaus,' Mok says. As an example, she cites how the council, told there was no land to build hostels, approached social welfare officials about converting disused special education schools into residential centres - but was told the Education Bureau would not allow it. 'There needs to be more co-ordination between governmental agencies,' says Lian, of the University of Hong Kong. 'Currently, it seems limited and they could do a lot more if they worked together. For instance, alongside the secondary school reform, the government could create a programme for people with mental disabilities. It's not just a formality, it's good preparation for them to live more independent lives later on.'

For parents and children forced to live apart because of age, the separation can be distressing, says Baptist University's Li, who has been conducting interviews with ageing parents of mentally disabled people.

'At some point, the parents become so frail they need to enter a nursing home while their mentally disabled children are put in a hostel. The problem is that nursing homes and hostels are usually very far apart. They're located in remote areas which are difficult for an elderly parent to access.'

Li gives the example of an 85-year-old man living in a nursing home who can only see his severely disabled 45-year-old son once a week. 'Both father and son only have this to look forward to. It is very sad,' he says.

Leung Siu-kun, executive director of Fu Hong Society, another NGO providing services to mentally disabled people, suggests 'parent-child dormitories' that combine supervision over parent and offspring. 'But these buildings need a lot more resources and manpower,' she says.

Liu Wong Shiu-king, 75, would appreciate that option. Because her daughter Mun-wah, 52, has severe mental disability, Liu used to work as a seamstress from home so she never had to leave her side. 'There were no services at the time,' she says. 'My husband provided for us financially, but he said if I wanted to keep [Mun-wah] I would have to take care of her myself.'

For 20 years Liu even carried her daughter on her back until her knees wore out. Mun-wah was later accepted at a day activity centre and five years ago secured a place in a Kwai Chung hostel. But because Liu, too, now walks with difficulty, she can only visit her daughter every fortnight.

'We were really lucky to have a placement so early on,' Liu says. 'But I still worry about Mun-wah when I pass away. I can't rely on relatives to visit her as often as I do.'