Motorists travelling along parts of Waianakarua Rd are being urged to take care along a specially marked portion of the road.
A 200-metre section of the road at Orere Point, south of Kakanui, has been reduced to one lane after parts of the shoulder broke away.
Waitaki District Council roading manager Michael Voss said the damage is due to coastal erosion.
"The road at this location has been undermined by the sea to the point where slippage has occurred and it is no longer safe to keep the two lanes open," he said.
"We are now fully assessing the situation to determine what the longer-term options are."
Mr Voss said semi-permanent railings and signage is in place.
"Our first priority is to ensure the area is as safe as possible for road users and before we undertake a full assessment with our contractors, SouthRoads," he said.
"I urge drivers to observe the temporary 30km/h speed limit and to drive in the marked lane.
"Vibration from vehicles travelling at higher speeds than the signed limit will certainly not be helpful to the overall situation."