Participants in the intervention group will receive a collaborative stepped care programme provided by registered social workers and trained Peer Supporters from aged care service units - the Districts Elderly Community Centres (DECC), and mental health service units - the Integrated Community Centre on Mental Wellness (ICCMW), all are local NGOs. In the collaborative stepped care model (see attachment Table 1), older persons are matched to the intervention module that most suits their current needs. The person does not have to start at the lowest level of intervention to progress to the next level of intervention. Rather, they enter the service with the intervention level aligned to their needs, e.g., level of risks, symptom severity (measured by the Patient Health Questionnaire, PHQ-9), and intervention response. Home visits or other format of contact will be delivered by trained Peer Supporters employed by the NGOs to detect and engage hidden cases.

Case identification will be done through open referral and outreach activities such as street booth, talks, and home visits.

For older adults with mild depressive symptoms (PHQ-9 score 5-9), 6-8 weeks of indicated prevention with psychoeducation or low-intensity psychotherapy would be provided by the project social workers in DECC. For participants with moderate depressive symptoms (PHQ-9 score 10-14), 6-8 weeks high-intensity clinical intervention, mainly group cognitive behavioral therapy (CBT), would be provided by project social workers from DECC and ICCMW. For those with moderately severe depressive symptoms (PHQ-9 score 15-19), 8-10 weeks individual CBT or group CBT at higher frequency would be provided by the project social workers from ICCMW.

In the progress review when a client is assessed to meet the discharge criteria, a 2-month exit plan involving a Peer Supporter follow-up is invoked.

Depression will be measured by the Patient Health Questionnaire (PHQ-9), a 9-item instrument that incorporates depression diagnostic criteria with other leading major depressive symptoms, and rates the frequency of the symptoms that factor into the scoring severity index. PHQ-9 total score ranges from 0 to 27, higher scores indicate higher levels of depression. Change scores of depression will be calculated by subtract the baseline PHQ-9 score from the follow-up PHQ-9 score, and negative results indicates reduction in depression.

Anxiety will be measured by the Generalized Anxiety Disorder scale (GAD-7), a 7-item scale in which responses to each item are rated on a 4-point Likert scale ranging from 0 to 3. The total score will be used, ranging from 0 to 21. Higher scores indicate higher levels of anxiety symptoms. Change scores of anxiety will be calculated by subtract the baseline GAD-7 score from the follow-up GAD-7 score, and negative results indicates reduction in anxiety.

Loneliness will be measured by the UCLA loneliness scale (UCLA-3), a 3-item self-report scale with each item evaluated with scores ranging from 0 (never) to 3 (often). The total score will be used, ranging from 0 to 9. Higher scores indicate greater loneliness. Change scores of loneliness will be calculated by subtract the baseline UCLA-3 score from the follow-up UCLA-3 score, and negative results indicates reduction in loneliness.

Self-harm risk will be assessed using eight items adapted from the Self-Harm Inventory, providing an overall assessment based on total score and clinical judgement. Social service staff assess participants' risk of self-harm (yes or no answers to 10 items) and harm to others (yes or no answers to 4 items). An overall evaluation of suicidal risk score ranges from 0 (No) to 3 (High). The overall evaluation score will be used. Change scores of self-harm risk will be calculated by subtract the baseline overall risk score from the follow-up risk score, and negative results indicates reduction in self-harm risk.

A semi-structured interview asking clients about their typical day activities in three domains: physical, social, and mental. A combination of being active in at least two domains would be used as one of the exit criteria. The changes of total numbers of activities reported will be calculated.