A preliminary audit has discovered about 20,000 endoscopy procedures may be overdue, sparking moves to expedite them.
NSW Health Minister Ryan Park on Saturday said the government would invest $17 million to rectify delays after the information "came to light".
The audit followed engagement with clinicians and patients about endoscopy wait times prompted NSW Health to collect data from across the health system.
Data was centrally monitored previously, according to the government.
Preliminary estimates found about 20,000 endoscopy procedures may be overdue, with final figures still to be validated.
"To patients and clinicians who have spoken of endoscopy wait times, you've been heard and NSW Health is acting," Mr Park said on Saturday.
"Our priority has always been ensuring we improve access to health care. When this came to light, we immediately took action to make sure communities are getting the care they need as quickly as possible."
Endoscopy is used to investigate, diagnose and monitor a range of health conditions and investigating possible bowel disease, including cancer.
About 350,000 endoscopies are performed in NSW each year across public and private facilities.
Wait times have been a longstanding challenge for the health system due to growing demand, an ageing population and increasing referrals through the National Bowel Cancer Screening Program and via other channels.
Cancer Council NSW chief executive Sarah Hosking said prolonged delays for procedures have long been a concern raised by patients.
"We are pleased to see action being taken," she said.
"We know early detection is vital.
"Bowel cancer is one of the most treatable cancers when detected early, so people who receive a positive screening result need timely access to the follow-up care they need."