A heritage tunnel south of Nelson which was re-opened this year as part of a cycle trail in the Tasman District, has been closed temporarily for structural improvements.
The Tasman council's engineering manager Peter Thomson said a routine geotechnical inspection found a problem at the northern entrance of the 125-year-old tunnel, which stretches for 1.4km.
He said further investigation was needed before he could confirm the nature of the problem but it was likely to be around the stability of some of the retaining work.
Mr Thomson said the two-week closure was a precautionary measure and arose from the council's responsibility for public safety.
"So what we found is some work which needs some further investigation, so it's a precautionary approach just to make sure that all of the structural components of the tunnel opening are safe.
The Spooners Tunnel was opened in 1893 to serve a rail link between Nelson and the West Coast.
It was closed in 1955 and reopened in April this year as part of the Taste Tasman Cycle Trail.
Much of the previously government-owned land for the trail was returned to Ngāti Toa, which had been supportive of the restoration.