Work to help prevent flooding at the intersection of Duke and George Sts had been expected to take two weeks to complete but was halted when Fulton Hogan contractors uncovered the stones on Monday. They were covered by tarseal.
Drainage manager Darren Waters said he had worked on a few sites in Dunedin where old items had been discovered but it was unusual to find sites of this size or significance.
''This is quite a rare find, as it is such a big piece in an intersection.''
Work had been stopped but the contractors would probably continue further along the road where there was no archaeological significance, Mr Waters said.
New Zealand Heritage Properties principal archaeologist Hayden Cawte said the area was a known archaeological site and an assessment should have been done before consent was granted.
A lack of oversight probably led to the mishap, he said.
Dunedin City Council engineering project manager Janan Nirainjanan said the council would decide what to do based on advice from an assessment by NZHP.
Potential solutions include covering or relocating the stones, in order to preserve them.
As the stones were believed to be from before 1900, they would be protected under the Historic Places Act 1993, which states it is illegal to damage or modify any archaeological site, he said.
Contractors could not resume work until the assessment and advice were completed.
The assessment could take up to 20 days to complete. However, the council intended to speed the process up to lessen the effect on traffic flow, Mr Nirainjanan said.
''We are trying to get the assessment done as quickly as possible.
''Once that is done, then maybe we can continue the work.''
Dr Cawte said he expected the consent process could take up to six weeks to complete.
Mr Nirainjanan said the exact age of the stones was yet to be determined.
It was likely they were part of an old road that continued down Duke St, he said.
According to the online database Archsite, Dunedin has hundreds of archaeological sites that were built since the city was founded in 1848.
by Samuel White
