"Farmers have been unable to grow sufficient feed for winter, and have been using stored feed and buying in supplements for stock, as well as selling off animals.
"Some useful rain is predicted for this week, however the drought has already taken its toll on farms and will take time to recover from.
"While rain now would allow pasture to grow, this can take a month to translate into feed for animals, and many are now well behind in preparing for winter," Mr O'Connor said.
The formal request for the classification was made by drought committees and rural communities yesterday in a letter to Mr O'Connor – which highlighted the stretch of dry weather was an "extremely unusual" event for Southland.
"Organisations in the regions are gearing up to assist farmers with feed budgets, technical information and farm management, and stress management.
"The early start to a hot dry summer has now taken its toll on the groundwater and rivers in the south of the country, and farmers are working hard to look after their animals in a very challenging climate."
The drought was originally classified as a medium-scale adverse event in the North Island across Taranaki, western parts of Manawatu-Whanganui and Wellington, and the Grey and Buller districts of the South Island's West Coast over the Christmas period.
Significant rain has improved soil moisture in some of those areas, but recovery from the drought is an ongoing process.