On Thursday, Sadag said in a statement that it was feeling "overwhelmed and inundated" with calls from people who felt completely helpless, hopeless and desperate for crisis intervention for depression and suicide.
"This week alone, we have had many additional suicide callers, concerned family members and even work colleagues calling in to ask for help, information and emergency intervention," it said.
"Our volunteer counsellors have been fielding hundreds of calls per shift, while more people have been reaching out via emails, SMSs and social media, needing help with various mental health issues."
It usually received up to 600 calls per day but the number had increased.
Sadag's suicide crisis helpline was not funded and was kept afloat through donations from private individuals or corporate companies.
Telephones calls could cost as much as R80 000 a month.
"This month, we will need more funds since we have received such an influx of calls, especially since 90% of our calls are toll-free."
Sadag shared some of the messages that it had recently received from people in despair.
One person said: "I'm alone and your organisation knows how this feels. I've taken out a life insurance and was planning to ram my car into a wall hoping it silences the talk in my head."
Another shared: "I don't want to live anymore. I am making everyone around me unhappy. I just want to end it all. I really don't want to feel this pain and heavy heart anymore. I need help to end it".
Sadag said its volunteer counsellors assisted callers who needed urgent hospitalisation or crisis intervention.
"This takes many resources, additional outgoing calls and a team of counsellors working on each case."
This comes after the death of top cardiologist Professor Bongani Mayosi.
Mayosi's family revealed shortly after his death on Friday that he had committed suicide after a long struggle with depression. He was 51.
Those who would like to help Sadag could contact 011 234 4837, email office@anxiety.org.za, or donate online via www.sadag.org.