Northland, Auckland, Waikato, Bay of Plenty and Hawkes Bay had already been declared to be in drought.
Wairarapa, Manawatu, Rangitikei, Taranaki, East Coast and Wellington have now been added to that list.
The drought is predicted to cost the economy $1 billion as hard-hit farmers struggle to feed stock.
Climate scientist Jim Salinger said yesterday the North Island had not experienced a drought so severe for 70 years and warned that such events could become more frequent. Cyclone Sandra is expected to bring rain to most places this weekend - the first decent fall since mid-January - with showers to follow on Monday.
Mr McLaren said "reasonable" rain in the next week or two weeks would still allow time for pasture growth to get cracking before cold nights affected it.
Metservice said south-westerly winds along the east coast of the North Island on Sunday combined with the remnants of tropical cyclone Sandy are expected to bring rain to Wairarapa on Sunday evening and Monday morning.
The rain is expected to ease to a few showers by Tuesday with dry conditions returning to the region by Wednesday and Thursday.
Mr Guy said it had become clear that nearly all farmers in every part of the North Island are facing very difficult dry conditions.
Rural assistance payments, equivalent to the unemployment benefit, would be available from Work and Income to those in extreme hardship.
"Many rural people can be reluctant to ask for help, but it is important for them to know that support is available," Mr Guy said.
"Some rain is forecast this weekend which is welcome news. However, we will need more than this to help prepare for the winter and set up for next spring."
Federated Farmers president Bruce Wills said he could not recall a time when the entire North Island had been in drought.
He said Government financial assistance would be a drop in the ocean compared to what farmers had lost or were going to lose but the emotional support the declaration offered was very welcome.
"These are people that are suffering through no fault of their own, through an act of God. We have real concerns about the emotional stress and difficulties that many families are coping with and that's the predominant benefit that comes from a drought declaration," Mr Wills said. "It doesn't mean any money directly to farmers, it's just about having some competent, expert people out there who are able to be at the end of the phone, or to sit around the kitchen table and talk it through."