The New Zealand Medical Association has told a parliamentary committee it opposes changing the law to allow voluntary euthanasia.
The health committee is gathering evidence in response to a petition asking for a law change.
A fortnight ago it heard from supporters of voluntary euthanasia, and on Tuesday it was the turn of those who oppose it.
Dr Stephen Child, chair of the NZMAA, told the committee the association represented 5500 medical professionals.
"Doctors do everything we possibly can for our patients ... but 10 to 15 percent of diagnoses are incorrect, and three percent of diagnoses of cancer are incorrect," he said.
"We're not always right in diagnosis, and we're not always right in prognosis.
"In principle and in practice, the association does not support a change in the legislation."
Dr Child said doctors believed in pain relief "even if the secondary consequences of that may hasten death ... giving morphine to a dying patient is not what we're talking about here".
The Care Alliance, a coalition of organisations and individuals opposed to voluntary euthanasia, said "assisted suicide" was unnecessary and dangerous.
"The right response to suffering is to continue the services for people with terminal illnesses," said the alliance's secretary, Matthew Jansen.
The Wellington Interfaith Council said all religions opposed the ending of life.
Council chairman Khalid Sandhu, a doctor, gave several examples of how his terminally ill patients had died peacefully under palliative care.
"We are desperate to stop people committing suicide, while at the same time discussing giving people that choice," he said.
The committee will continue hearing submissions, and then report to parliament.