Tourism West Coast says the closure of State Highway 6 has resulted in mass cancellations for tourism operators and could not have come at a worse time.
Floodwaters this week washed away 40 metres of road leading to a one-lane bridge just north of Harihari, forcing travellers to take lengthy detours. Assessors say the bridge itself appears sound.
Tourism West Coast chief executive Jim Little says the washout has affected the entire West Coast of the South Island.
"It's impacting both ways, because those coming from Queenstown and Wanaka are now diverting through the Mackenzie country and those coming down from the north are cutting back across Arthur's Pass. So it's obviously having a big impact on places like Hokitika as well."
Mr Little says the Franz Josef and Fox glaciers have been particularly affected, with one business noticing a 90% reduction in turnover.
He says it is the peak time of year for operators and, after a slow season last summer, the disruption is the last thing they need.
Mr Little says although the closure has hit tourism hard, the two main bus operators have continued bringing passengers to the West Coast via lengthy detours, which has helped.
NZTA hopes to have SH6 reopen on Tuesday
The New Zealand Transport Agency says it plans to have State Highway 6 reopened by midday on Tuesday if the weather cooperates.
Mr Little says the timeline means tour groups can start rebooking their stops along the coast for next week.
The only other road closure in the South Island is State Highway 65 from O'Sullivans to Springs Junction.
Meanwhile, KiwiRail says slips covering the tracks mean it will be three or four days before its Tranz Alpine freight and passenger service between Christchurch and Greymouth resumes.
Buses that train passengers can use are now travelling a similar route.
Meanwhile, Bernard May, general manager of the Westland Milk Products processing plant in Hokitika, says some dairy farmers unable to get their milk through to the plant have started dumping it.
Work begins to divert river
Contractors began working on Friday to divert the flooded Wanganui River that washed out part of State Highway 6.
The Transport Agency's West Coast area manager, Mark Pinner, told Radio New Zealand's Summer Report programme on Friday that the rainfall completely threw the river off its original course.
"The sheer volume that's come down - we're taking five or six hundred millimetres of rain in a day or two - it came down off these steep hills.
"It's just basically got so much force it's just created its own new direction and, unfortunately, it's taken a new path beyond the bridge and it's taken the road approach to the bridge away of about 40 to 50 metres."
Workers will use large rocks and dig a channel in order to divert the river back to its original course.
Mr Pinner says contractors will then rebuild a rudimentary road up to the bridge to get traffic flowing once more, but it will still be several days before the highway opens.
Water levels dropped about one metre overnight on Thursday, but the river is still too high for structural engineers to make a detailed inspection of the bridge.
Listen to Summer Report interview with Mark Pinner