Hawke's Bay topped the growth charts, climbing 14 per cent on last year to a record $400 per week.
Whangarei's One Double Five Community House co-ordinator Carol Peters said families struggling to make ends meet were spending almost half of their income on rents.
"That then reduces the amount of money they have for food and other expenses like petrol costs if they have a vehicle and this has been a trend for 20 years and it's getting worse."
She said the poor and unemployed were particularly affected by high rents. Those who did not qualify for rental supplement were also badly affected.
Paul Beazley of L J Hooker in Whangarei said rents were purely dictated by supply and demand.
He said the Northland rental market, particularly Whangarei, was the same as other parts of New Zealand and had been steadily climbing which put pressure on tenants.
The median rent in Northland in January was $385 dropping slightly to $380 in February before increasing to $400 last month.
In the Far North, the median rent in January was $365 going up to $390 before falling to $320 in March. Kaipara's median rent was $320 in January, $375 in February and $385 in March.