Buller and Grey Districts have become the first areas of the South Island to be declared drought zones, and rain is still 10 days away.
Minister for Primary Industries Nathan Guy said the rain in the last week had not been enough to help these districts, and only limited rain was forecast for the next two weeks.
"It is very unusual for the West Coast to experience drought conditions and is not something that local farmers are used to. It shows just how extreme this dry period has been.
"Conditions have deteriorated quickly, and local farmers have asked the Government to recognise the tough situation they are facing.''
The drought declaration means that Government assistance will be available to affected farmers.
Federated Farmers' West Coast provincial president Katie Milne welcomed the drought declaration.
"The reality is that we have basically used up our winter feed in summer and autumn and the cupboard is bare for winter,'' she said.
The entire North Island is now officially in a state of drought, and the declaration of drought in the south comes despite some moderate rain this week.
Federated Farmers' vice-president William Rolleston, who farms in south Canterbury, said the West Coast was "by far'' the worst hit region in the South Island, and he was hopeful other regions would not follow suit.
Climate scientist Brett Mullan said this year's drought was the worst in 41 years in the West Coast as well as Northland, Auckland, Waikato, Bay of Plenty, Gisborne and Hawkes Bay, and the worst or equal for the country in 70 years.
Dr Mullan said weather models forecast a rain-bearing front from the Tasman Sea in the next 10 days.
"It appears it will drop some rain over the West Coast of New Zealand from Sunday [March 31] through to Tuesday, but not a lot of relief for the North Island districts.''
There was still no clue as to when the drought would be declared over.
The 2008 drought broke in April, but the drought in 2010 did not break until May, Dr Mullan said.
"In the North Island, at least, it gets wetter as you go into winter and it's a very noticeable trend, but it's not the same for the South Island.''
Climate scientist Andrew Tait said as autumn takes hold with its cooler temperatures, the amount of drying through the day with evaporation was starting to decrease.
Dew on the ground made a difference to moisture levels too.
"I think the peak of the drought has passed, but ... it's very difficult to say when it might be over for good.''
(MPI) Resource Policy North Island regions manager Stuart Anderson said a range of factors needed to be considered before declaring an end to the drought.
"How the soil moisture has recovered, what grass cover there is ... and most importantly, how farmers are at in terms of being able to manage themselves through the impact.
"So it's not entirely clear cut in terms of one measure or the other.''
Dr Tait said just before rain fell last Saturday morning much of the North Island had reached its dry peak.
"Through Waikato, eastern areas, Northland and Auckland were still very dry.''
However, the rain that fell for three days "had quite a bit of influence''.
The soil has maintained moisture since Wednesday, Dr Tait said.
But he said it would take more rainfall through the rest of March and April before soil moisture levels returned to where they were this time last year.
"That's a key consideration, thinking about how long this drought's going to last.''