Vacancies remain for 60 full-time registered nurse positions at the city's main mental health facilities.
The Canterbury District Health Board (CDHB) revealed in its monthly meeting that staffing challenges and options were being addressed.
An anonymous mental health nurse said those in the workforce frequently covered extra hours and shifts on their days off.
"On another occasion I worked 64 hours in four days," he said.
Despite the CDHB having addressed the staffing issues, it failed to contribute any of its mental health budget to staffing and recruitment.
AJ, the brother of a frequent patient of mental health services, said he felt the shortage of trained professionals is having a negative impact on the quality of care.
"I think it's terrible... the best option is getting people, who have some good work qualifications and actually know what they're doing," AJ said.
"If there isn't enough people, I guess they wouldn't be able to be more efficient."
The government announced earlier in the year that $1.9 billion would be put towards mental health, inclusive of $200 million earmarked for existing facilities.