Peter Emtage told councillors last week that evidence from other mining towns was tunnels could collapse unexpectedly, and mapping would show which private, public or council-owned land or buildings might be at risk.
Hiring consultants to map the area using the latest technology, a 3-D ground penetrating radar scanner, would get ''direct, unequivocal clear results'', he said.
''Residents want to know their investment [in their properties] will be there into the future.''
Ohai, about 65km northwest of Invercargill, was a significant coalmining area for more than 90 years until the last remaining large mine closed in 2009.
Mr Emtage said he had seen maps and other information which showed tunnels 30m-35m below the surface of the eastern part of the town and about 110m deep under the western part of the town.
No tunnels had subsided or collapsed in the 10 years he had lived there, but he said he had been told of ''sinkage'' about 20 years ago at a private home and at the original school.
The potential hazard from collapsing tunnels was discouraging people from buying in the town he said. The population had dropped by about 20% in the past 15 years and now sat at about 350.
''My aim is to get clarification of exactly what's under us. If it is bad news, we can move forward from there. If it is good news, we can get that out to the people ... and encourage growth.''
Southland Mayor Frana Cardno asked why present-day ratepayers should fund the mapping when the tunnels were dug ''a long time back'' before the council existed.
Mr Emtage said he believed the council should pay for the good of the town. But if mapping showed a potential hazard, ongoing liability and accountability should lie with the Government.
A 3-D scanner cost $16,000 to buy, he said, but he did not know how much it would cost to hire one for several days.
Councillors called for a staff report into the issue.
