Police are investigating a serious domestic assault that left a Northland woman fighting for her life.

The incident occurred on Tuesday evening at a home in Opononi, where St John Ambulance medics found a 42-year-old woman with life-threatening injuries.

She was flown to Whangarei Hospital in a critical condition by the Northland Electricity Rescue Helicopter.

She was yesterday still in the hospital's intensive care unit where her condition was described as stable. Detective Sergeant Chris Fouhy, of Kaikohe police, said a suspect was interviewed later that evening and again yesterday morning.

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It was not yet certain whether a weapon had been used.

Police were continuing to interview witnesses and trying to piece together the evening's events, Mr Fouhy said.

Northland has an unenviable record for serious domestic assaults, several of which been fatal.

A report last year found that Northland had the country's second highest rate of deaths due to family violence.