"Farmers have been working hard and preparing for these conditions, but things are getting tough and there is little rain forecast for the next couple of weeks," Guy said.
There has been significant soil moisture deficits, low pasture covers, low supplementary feed, and maize crops have struggled, he said.
Guy said the Inland Revenue Department would also be exercising its income equalisation discretion to help provide flexibility and relief for drought-affected farmers.
"The Government is also keeping a very close eye on many parts of the East Coast of the North Island and supporting North Canterbury in their recovery."
Guy made the announcement today while visiting a dairy farm near Kerikeri.
Federated Farmers said the Government's decision to declare a medium-scale adverse event in Northland was "pragmatic and necessary".
Farmers were increasingly seeking advice and help in what was rapidly becoming a distressing situation, the farmers group said.
Federated Farmers' Northland Provincial President John Blackwell said the situation "definitely warranted action".
"The Northland Rural Support Trust is in no doubt; they have been through similar scenarios in recent years," Blackwell said.
"From reviewing those past events, they've come to the conclusion that they could have intervened sooner," he said.
Blackwell said the declaration would facilitate modest financial support towards counselling and advisory services, with flexibility around tax for those worst affected.
