The procedure went ahead at 9pm with what Mr Reeves described as "unseemly haste". The 20-year-old woman died soon after.
Northland District Health Board's chief medical officer Michael Roberts would only confirm the case has been reported to the coroner.
"As with all unexpected deaths the case has been reported to the coroner. The DHB is confident that the coroner's investigation will determine the care provided to the patient was appropriate," Dr Roberts said.
The DHB has not responded to other questions about protocols regarding the termination of life support.
Mr Reeves said he asked for the delay so he could "get the matter before a judge the next day".
A practising barrister and solicitor for 40 years, he said he was told by someone he believed to be an intensive care doctor that they could not talk with him. The person said she had "looked him up" and he was not on the New Zealand Law Registry.
He had not heard back from either the hospital or his client that evening.
"I'm shocked because all they needed to do was put it off for a day while a judge looked at the case," he said.
"There is always the difficulty a judge might say it is not the law's job to make medical decisions but at least we'd have tried."
The patient's mother had wanted other medical opinions about her daughter, who had been admitted with respiratory failure.
She telephoned the Northern Advocate shortly before the machines were turned off, desperate to bring attention to the situation.
"Too many snap decisions are being made. They're not giving us time. There has been no consent given for what has happened to [her daughter] or her baby," the woman said.
She was distraught not only about her daughter's imminent death but over the death of the three-week premature baby who was airlifted to Auckland Hospital after being delivered by emergency caesarean at Whangarei Hospital the day before. The baby died soon after arrival there, she said.
It is understood the 20-year-old pregnant woman was having a severe asthma attack and had been rushed by emergency helicopter to Whangarei from another Northland town, before having the caesarean delivery.
Northland Police spokeswoman Sarah Kennett confirmed the police were notified of the death of a 20-year-old woman at the hospital on Wednesday night and the case was now in the hands of the coroner.