The Department of Planning, Transport and Infrastructure has a sinking feeling about East Terrace, Murray Bridge.
The reason the road was closed last week, and will be repaired on Thursday, is "pavement surface subsiding", according to a departmental spokesman.
He did not say whether the caution was prompted by the fact a railway tunnel on the main Adelaide to Melbourne line passes beneath East Terrace's intersection with Bridge Street.
The road will reopen as soon as the repairs are complete.
The Murray Bridge council said it was an unfortunate coincidence that separate road works a few metres around the corner on South Terrace, long planned, were now going ahead at the same time.
Infrastructure and assets general manager Heather Barclay said power lines were being put underground on that street.
The works will be finished before the end of June.
They were originally due immediately after an upgrade of nearby Sixth Street, but the council delayed them to avoid disrupting traders for a prolonged period.
Note: An earlier version of this story gave an incorrect surname for the council’s spokeswoman.