Family members attempted to resuscitate the girl but were unsuccessful, Ms Kennett said.
She said emergency services staff attempted to resuscitate the girl for an hour.
Two ambulances, a doctor, an appliance from Dargaville Volunteer Fire Brigade and a Northland Emergency Services Helicopter attended, a St John spokesman said.
It was unclear who was at the house at the time but it was believed both parents were present, Ms Kennett said.
The death has been referred to the coroner.
Last year 12 people died in Northland waters, two fewer than in 2013, but there have been six suspected drownings already this year in the region.
Water Safety New Zealand chief executive Matt Claridge said Northland's drowning toll was the highest in the country per capita.
The region's huge coastline, access to the sea - never more than 30 minutes from a beach in the region - and high tourist numbers, played a part in that, Mr Claridge said.
Monday's drowning was the second toddler to drown in Northland in just over a year. On February 24, 2014, 18-month-old Ebana Brough drowned in the Waipapakauri Creek.
