The accident happened near a camping ground in Kellys Bay, on the Kaipara Harbour south of Dargaville.
A spokeswoman at the Kellys Bay Camping Reserve confirmed the couple had been staying at the camp, but did not want to comment further.
It is understood the pair were regular visitors to the camp ground.
A resident in nearby Kellys Bay Road told the Herald police were still at the scene of the accident, which is thought to involve two adults.
"We haven't heard anything, but police are still there. We're just keeping well away,'' she said.
Police said they were still waiting for an update from officers on the ground. The somewhat remote location of the accident meant there would be some delays.
Quad bike accidents
April 2015: Robert McKenzie, 14, died from injuries after a quad bike rolled into a ditch and trapped him on a farm near Kaikohe.
April 2015: Farmer Hamish McLennan, 56, died after his quad bike rolled on him on his dairy farm near Carterton.
January 2015: Lower Hutt girl Abigail Jane Schmal-Singleton, 6, died after the child-sized quad bike she was riding crashed into a fence in Wairarapa.
December 2014: A farm worker died after the quad bike he was riding rolled down a slope in Dannevirke.
October 2012: Shane White, 10, died after being found pinned under a quad bike on the Wairarapa farm where his family were sharemilkers.
October 2012: Aussie Chelsey Callaghan, 37, died after crashing in Tuakau.