The shaken couple returned to Punakaiki and raised the alarm.
Authorities say the road may not reopen until Wednesday.
Meybille Bay, a narrow area of the Coast Road a few kilometres north of Punakaiki, has been prone to slips in the past. The trip from Punakaiki to Westport takes over two hours via Reefton, compared to about 40 minutes on SH6.
Once news filtered out a steady stream of locals turned up on both sides of the slip throughout the afternoon to check what was happening.
One Coast Road resident, Brady Lindbom, borrowed traffic cones from a Woodpecker Bay resident and sat near the slip on the Fox River side for about two- and-a- half hours to warn motorists before road crews arrived.
Overnight falls
New Zealand Transport Agency (NZTA) regional performance manager, Pete Connors said more debris fell overnight with around 2500 cubic metres of rock, earth and vegetation piled up on the road this morning.
He said four trucks and one digger were brought in to work the Punakaiki side while five trucks and two diggers were clearing from the Fox River end.
Contractors began by sluicing to remove loose material and rocks off the road then the diggers loaded up truckload after truckload of rock and earth.
Mr Connors said material removed from the Punakaiki side was taken to the Punakaiki Beach Camp where the West Coast Regional Council would reuse some of the rock in the sea wall extension.
Rock from the Fox River side was taken for storage in a local quarry.
Mr Connors said the road was unlikely to open today.
"The safety of road users is paramount and the road will not be reopened until contract teams and geotechnical advisors are confident it is safe."
Punakaiki impact
Most vehicle traffic on SH6 around Punakaiki today was contractors' trucks hauling away debris and locals moving about.
No bus services were coming in or out due to diversions in place at the Westport crossroads (SH67-SH6 junction) and at Rapahoe.
Workers from Fox River who travel to Greymouth each day were unable to make the commute this morning and it was the same for those in Punakaiki who work in Westport.
The Department of Conservation's (DOC) visitor centre had just one customer when The News visited - an Australian seeking information about how to get to Picton via the diversion. (He also reported to DOC that he was very confident that he had seen two kiwis on the road nearby.)
The Punakaiki Craft Shop was empty apart from two staff members who said they expected a very quiet day due to the usual buses being diverted.
At the Punakaiki Beach Camp Sue Findlay said they had been averaging 30 guests per night in September, which was very good for this time of year, but they were down to just four people last night.
Other accommodation providers contacted said they had noticed no difference in bookings so far but were relieved the slip had happened now rather than the really busy summer months.
Long way home
Westport's Noelene Richards, her husband Paul and a friend had to take the long way home.
They were having lunch in Punakaiki after doing a bush walk when they learned of the slip.
"We were sitting at the hotel enjoying our lunch...then someone came in and said 'who's going to Westport?' We said 'we're going to Westport' he said, 'no you're not'."
Before setting off for Greymouth, they drove to the slip site to take a look.
"It was massive...it looks like it might have taken a bit of the road as it came down.
"We were surprised that there was no sign in Greymouth or anywhere down that way saying the road was closed."
Many people, especially tourists, got all the way to the slip site before realising they had to turn around and go back, she said.
"Even the O'Conor Home van had to go back. It got right to the slip."
NZTA said contractors placed detour signs/roadblocks at Rapahoe, north of Greymouth and south of Westport at the intersection of SH6 and 7 just after 3pm yesterday.
Mrs Richards said she didn't mind having to take the long way home - she was in no hurry.
"It was a beautiful day."
She offered to take Westport-bound passengers travelling on an Intercity bus with her, but the driver said there weren't any, she said.
The slip caused a minor logistical headache for Hokitika-based Westland Milk Products (WMP). Tanker drivers picking up milk in the Buller District were forced to detour through Reefton and the Grey Valley, adding one hour maximum to their journey, said chief executive Toni Brendish.
St John Buller territorial manager Robbie Blankenstein said the slip had not affected St John operations. It had not received any requests to transfer patients from Buller Hospital to Grey Base Hospital, nor had it received any emergency callouts.
If a patient had a life-threatening condition/injury, a helicopter was used to transfer them to Greymouth anyway, he said. Luckily it was a good day for flying.
If necessary, ambulances transporting patients with non-life threatening injuries/conditions would take the detour route through Reefton, he said.
West Coast District Health Board general manager, Buller, Kathleen Gavigan, confirmed no patients had required transfers since the slip closed the road.
Three staff booked for a four-day professional development/training course had had to detour via Reefton to Greymouth, she said.
Freight and courier operators were philosophical.
Johnson Bros Transport dispatch manager Paul Power said a couple of their trucks had had to go the long way through Reefton yesterday and again today with general freight.
"You leave earlier, it does cost us a little bit though - it's an extra 50km to go the other way."
Grey Valley Couriers operations manager Tim Bailey said they didn't service Punakaiki today. Two or three of their vans had travelled via Reefton.
"It's just one those things," he said.
By Teresa Smith, Aimee van der Weyden and Lee Scanlon of the Westport News
