The sinkhole in Bootham Terrace, Clifton, has led to the partial closure of the footway.
Workers are now on the scene at the popular through-route to York station and are trying to rectify the issue.
Signs in the street instruct non-residents to walk down Queen Annes Road.
Steve Wragg, head of highway asset management at City of York Council, said the cause of the sinkhole remains a mystery.
He said: “City of York Council highways teams have carried out a range of investigations alongside Yorkshire Water to try to identify how the footway and carriageway on Bootham Terrace has sunk in a number of places.
“CCTV and other remote investigations have not been able to identify the cause, we are currently on site excavating to inspect the below ground conditions and will move to a second location next week.
“The cause of issues such as this can often be difficult to locate and we will continue to work with Yorkshire Water to isolate the issue and where necessary undertake works to reduce the chances of this happening again.”
