A sinkhole measuring 20m in diameter has been found on reserve land in Waihi.
Hauraki District Council chief executive Langley Cavers said the sinkhole was found this morning on a council reserve between the Waihi Rugby Club and the Martha open pit mine.
Cavers said the site, known to be above historic mine workings, was classified as a hazard zone in 2002 and was cordoned off.
"While this is inconvenient, it is within an area where sinkholes could be expected."
The sinkhole collapsed into a partially filled stope in the historic Royal workings within the high hazard zone.
Original records indicated the upper 20m of the historic stope remained unfilled.
Cavers said the area around the sinkhole, including the Pit Rim Walkway, had been cordoned off. Access to the walkway was still possible next to nearby pensioner flats.
He said council staff had visited the occupants of the flats and told them about the sinkhole.
There were no concerns for the safety of the residents or about ground stability in that area.
Council engineers are working with the mine owner OceanaGold's engineers to investigate remediation options.
OceanaGold senior community advisor Kit Wilson said it was the first sinkhole to appear since a huge one in 2001 swallowed a house and part of Seddon St.
The new sinkhole was nearby but much smaller.
"This is directly over what would have been Seddon St back in 2001. It is surprising but not unexpected."
He said the company would help fix the hole.