The Hokitika River was threatening to sweep away a campervan parked on one of the braided river's islands.
Westland District Council mayor Bruce Smith said the second alarm for the river had been activated, and there was still another few hundred millimetres of rain forecast.
He says the first alarm is when it hits a level that is considered a flood, the third is extreme and if that goes off they will have some problems "for sure".
Civil Defence has been activated in Westland as heavy rain hammers the West Coast.
π§οΈ Extreme rainfall totals in the South Island π§οΈ
π Ivory Glacier 391 mm [more than Clyde, Cromwell & Alexandra saw in the entire year of 2017!] π Mt Philistine 294 mm π Mt Cook 212 mm pic.twitter.com/SH5rPuNOTI
Flooding at Deep Creek Road Moana, on the West Coast of the South Island. Photo / Supplied
The conditions have caused parts of roads on the West Coast to crumble and fall away, forcing the NZ Transport Agency to close main highways.
State Highway 6 from Hokitika to Haast and State Highway 73 Arthurs Pass between Arthurs Pass township and Jackson will likely remain closed overnight.
Drivers in the area are being urged by NZTA not to travel unless it is absolutely essential.
The following Roads are currently CLOSED due to weather conditions: SH73 Arthurs Pass to Jackson SH6 Harihari to Fox Glacier SH6 Hokitika to Harihari
For all South Island warnings please check our Traffic Map for details. ^JPhttps://t.co/cpWPeIXZBe
— Waka Kotahi NZTA Canterbury & West Coast (@WakaKotahiCWC) November 8, 2018
"If the road remains closed overnight, a full assessment of the route will be made at first light tomorrow," NZTA Regional Systems Manager Pete Connors said.
"It is still raining steadily in the region, and there is widespread surface flooding and several slips that our crews have been unable access.
"The situation is being constantly assessed, and our primary consideration is the safety of road users, as well as the safety of crews working to clear slips and unblock culverts."
MetService meteorologist Gerrit Keyser said at about 11am the highest rainfall totals for the past 12 hours were in Arthur's Pass with 112mm, Mt Cook Village with 102mm, Franz Josef with 81.5mm and Milford with 75mm.
Flooding at Okuru River on the West Coast. Photo / Kerry Eggeling
Strong winds were also starting to ramp up about the Canterbury high country, Wellington and southern Wairarapa. Gusts could reach 150km/h in exposed parts of Canterbury, and 130km/h in other affected areas.
The strongest winds recorded so far were 80km/h at a station near Lumsden in Southland, and 65km/h at Le Bons Bay on Banks Peninsula.