Westland's mayor Helen Lash says the region has fared exceptionally well overnight and avoided the worst of the deluge.

A state of emergency remains in place but a red heavy rain warning has expired.

"We're very very fortunate because if we'd had the intensities for the length of time it was forecasted, we would be having a totally different conversation right now," Lash said.

The original forecast was for some areas to receive up to 49 millimetres an hour overnight and while the rain fell, it was spread over a longer period, she said.

Instead, rivers were beginning to fall and Lash said the slips that had been found were minor and were being cleaned up.

Nobody was evacuated overnight despite communities opening their halls ready to welcome anybody in need, Lash said.

"Everything worked like a well-oiled machine, I couldn't be more pleased with how everything worked."

State Highway 6 between Haast and Hokitika has now reopened following the two-day deluge.

Residents in parts of Westland were last night told to prepare to move at short notice, as torrential rain continues, and the worst yet to come.

A local State of Emergency had been declared for Westland between Hokitika and Haast.

Westland remained under a red heavy rain alert until 8am Saturday, with another band of heavy rain due to hit from 10pm.

In an 8.30pm update, MetService said on top of what had already fallen, 150mm-250mm of rain was expected to accumulate about the ranges, and possibly more in localised areas. It expected 40m-100mm of rain about the coast.

The Grey District is under an orange heavy rain warning until 9am Saturday with peak hourly rates of 25mm-30mm expected, especially Saturday morning.

The headwaters of Canterbury lakes and rivers from Arthur's Pass southwards are under a orange heavy rain warning until 6am Saturday.

"On top of what has already fallen, expect 100 to 200mm of rain near the Divide, with 50 to 100mm of rain spreading 15 km east of the Divide. Rainfall rates near the Divide could reach 20 to 30mm/h," MetService said.

SH6 from Ross to Makarora is closed and will remain closed overnight.

Earlier on Friday evening, West Coast Emergency Management said the expected rain would likely cause dangerous river conditions and significant flooding.

Slips and floodwaters were likely to make some roads impassable and could isolate communities, it said on Facebook.

Mayor Helen Lash said no evacuations had been necessary as of 8pm.

Though residents were being told to be prepared to move at short notice, as torrential rain continues, and the worst yet to come.

The Waiho River in Franz Josef is expected to peak around 2am, with the Hokitika River expected to follow around 10am.

High tide in Hokitika would be around 7am Saturday.

The rivers are being closely monitored overnight and Lash said if there was any risk to people, they will be advised to move accordingly.

Civil Defence has advised locals to stay home while guests staying in motels and hotels have been told to stay put.

Earlier, people camping near waterways were told to pack up and head to the nearest township for safe and secure accommodation.

Civil Defence will advise when the State of Emergency is lifted.

Overnight road conditions can be found on the Waka Kotahi NZTA website.

Minister for Civil Defence Mark Mitchell travelled to the West Coast this evening.

Main image: From top left: A spectator on the Waiho bailey bridge on SH6, near Franz Josef; the Tatare River near Franz Josef as seen from SH6; Roaring Billy Falls in Haast Valley and the state of emergency sign in Fox Glacier. Photo: RNZ / Tess Brunton / Martin Gibson