It is always good practice to network support by including trained professionals where possible. So, when meeting with a student who is at risk or in crisis you want to mentally sort through the best person or service to get involved.
Familiarise yourself with the internal services that are available within the university, for example, student support, counselling service, mental health advisory service, student support (which usually includes the disability support team, international students support, housing), the Students’ Union (which sometimes have helpline services), student health (for medically related support) etc.
It may be useful if you are in doubt, to clarify what these services can help with, and how to refer students to them by contacting the respective service or department.
If your university has a Counselling Service, it is worth finding out what they can offer in more urgent situations. Some might offer a drop-in type appointment, or emergency appointments, whereas others might be able to point you in the direction of other key services.
Often these services are familiar with the support systems in place in the university and can provide guidance to help you support the student.
There are many resources external to the university available in the community that are valuable for support, for example, the student's GP, A&E, Samaritans (phone and email support), local counselling provisions, police, etc. Medical services, such as GPs and hospitals offer emergency support both in office hours as well as out of hours.
As a general rule, always work within your limits of training and ability and, unless it is an emergency, attempt to utilise the internal support systems as there are stronger links through these services to establishing the external support services.