The heaviest rain in a deluge set to hit Westland is now expected to arrive on Friday evening.

Officials are trying to work out whether to evacuate homes before dark as a precaution.

A heavy rain red warning is in place for the region, until Saturday morning, with 500 to 700 mm of rain expected to accumulate about the ranges, and 100 to 200 mm about the coast.

Westland Mayor Helen Lash said Friday afternoon’s rain levels will be critical for the region from Haast to Hokitika, with another 300mm of rain expected in the ranges on top of what has already fallen. The worst of it is expected between 10pm Friday and 6am Saturday.