Two major slips following periods of heavy rainfall and a shallow magnitude-5.2 earthquake have occurred recently at a site about 2km south of the Boundary Creek reserve.
New Zealand Transport Agency Central Otago area manager John Jarvis said on September 5, two days after the nearby earthquake, the first slip spilled between 1000cu m and 2000cu m of rocks and large boulders on to the highway below. A second smaller slip happened on Saturday night.
Both times, the highway was completely closed the following day while Opus geotechnical engineers and Fulton Hogan workers worked to stabilise the bluff above and clear material from the road.
Yesterday, the highway was open to single-lane traffic with minor delays, however, it was closed completely again at 7pm, with the intention of reopening it again at 7am today.
"It's got to a point where it's too dangerous to have it open at night time," Mr Jarvis said.
"The slip's moved about another 50m up into the hillside than what it was last week and cracks have opened up and it's got a lot bigger over the last few days.
"We've made the decision in light of safety there's too many risks in leaving the road open overnight."
It was hoped a helicopter with a monsoon bucket would be brought in this morning to "trigger off some of the larger areas above that are hanging down".
Mr Jarvis said with further bad weather forecast over the next few days, it was unlikely the situation would be resolved any time soon.
"We'll continue reviewing those night-time closures but it's likely that will be in force for the next few nights.
"But the good news is that we can maintain traffic flow during the day ... at best it's going to be single-lane for some time."
