If doctor-assisted suicide was legalised disabled and vulnerable people would be placed in danger, an anti-euthanasia group has told a court today.

Care Alliance has made submissions in the High Court at Wellington where a potentially groundbreaking civil case over the legality of doctor-assisted death has been heard.

Lecretia Seales, 42, is dying from an inoperable brain tumour and is fighting a legal battle to be able to legally have her doctor assist in her death should her life become too unbearable.

If Justice David Collins rules in favour of Ms Seales, there could be a wide-ranging impact on others suffering a terminal illness.

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Care Alliance lawyer Victoria Casey said disabled people, including children were being euthanised in other countries.

In the Netherlands, in 2013, 97 people with dementia were euthanised, she said.

The Oregon legislation, which was being proposed in Ms Seales' case, had no provision for supervising the conditions in which lethal medication was taken and whether it was being taken freely.

In New Zealand there was a documented problem with elder abuse and the results of legalising doctor-assisted deaths could be "chilling", Ms Casey said.

She also strongly objected to Ms Seales' lawyers describing physical disability that their client might succumb to as degrading and lacking in dignity with many people suffering the same types of disabilities.

The legislation would put those people in danger, she said.

However, Voluntary Euthanasia Society lawyer Kate Davenport, QC, said legalising doctor-assisted death would not open the floodgates for people to be killed.

She said the civil case was about Ms Seales and the treatment she was seeking from her doctor.

Her doctor would prescribe medication for the purpose of relieving Ms Seales' suffering, Ms Davenport said.

The decision of when to take the medication would lie with Ms Seales, she said.

Earlier today the Crown finished its argument that there was nothing in current legislation that allowed for doctors to lawfully help to end someone's life and only a change in legislation would make it legal.

Professor Paul Rishworth, QC, said Ms Seales' arguments around who could apply for doctor-assisted death led to a slippery slope.

He pointed to people who suffered dementia and Huntington's disease could argue the law would apply to them.

The courts would also have to grapple with terminology such "terminal".

Some patients could live a "very long time" with terminal illnesses, he said.

"There is certainly a potential for a category creep or a slippery slope."

Ms Seales, a former lawyer, is relying on provisions in the Bill of Rights Act enshrining the rights to not be deprived of life or subjected to cruel treatment.

Ms Seales was not present for most of the day's court session.

During the duration of the hearing, the public gallery has been packed with members of the public and a handful of Ms Seales' supporters were seated in the jury box.

Justice Collins reserved his decision.