A whistleblower has claimed that the New South Wales healthcare watchdog is failing to properly assess hundreds of patients' complaints because of "a dysfunctional workplace culture".

The Health Care Complaints Commission (HCCC) is an independent government body that assesses, investigates and prosecutes medical complaints throughout the state.

The whistleblower, who spoke under anonymity, warned the mounting delays and administrative mistakes potentially "jeopardise public health and safety", and have triggered the departure of many senior staff with "decades of experience", with around 50 staff members resigning over the last three years.