Catholics in Colorado have reacted with dismay after the state voted to legalise assisted suicide.

The vote on legalisation, which came on the same day – Tuesday – as the presidential election, was approved by a margin of 65 per cent to 35 per cent.

Catholic, Mormon, and evangelical leaders played a role in the unsuccessful opposition to the ballot measure.

The Catholic News Agency (CNA) reported the Colorado Catholic Conference as saying yesterday: "The mission we have as citizens of Colorado should be to help people live with dignity – not to offer them more options to kill themselves."

The conference said the legalisation was "a great travesty of compassion and choice for the sick, the poor, the elderly and our most vulnerable residents".

The ballot measure, which is modelled on a 22-year-old Oregon law and uses the language of "medical aid in dying," is called the Colorado End-of-Life Options Act. It will allow an adult with a terminal illness to request a lethal prescription from their doctor. The individual must be deemed mentally competent and two doctors must diagnosis the person as having six months or fewer to live. The measure requires self-administration of the drug, called secobarbital, which is also used for lethal injections in some states, CNS said.

The measure voted on requires the official cause of death to be listed as a patient's underlying condition, not as an assisted suicide.

The president of the legal assisted suicide advocacy group Compassion and Choices, Barbara Coombs, said the vote was "an especially tremendous victory for terminally ill adults who worry about horrific suffering in their final days," the Associated Press reported.

But Colorado's Catholic Conference rejected depictions of assisted suicide as a private choice, saying: "killing, no matter what its motives, is never a private matter; it always impacts other people and has much wider implications."

The Conference added: "As Pope Francis has noted it only furthers a 'throwaway' culture".

A Colorado-based non-profit hospice and palliative health care provider, Divine Mercy Supportive Care, declared itself a "no-kill provider" in the wake of the vote. The Catholic organisation's policies follow the US bishops' ethical and religious directives for Catholic health care.

The organisation said it was "the antidote to assisted suicide." It added that advances in pain and symptom management have helped alleviate the suffering of advanced illness.

However, it said several other Colorado hospice agencies have said that they are willing to accommodate assisted suicide.

Supporters of legal assisted suicide failed to pass bills in the Colorado legislature in 2015 and 2016, before placing the proposal on the election day ballot.

According to the Denver Post, the ballot measure's advocates raised $4.8 million from groups like the Compassion & Choices Action Network.

Church groups opposed to the ballot measure raised $2.3 million, including contributions from the dioceses of Denver, St. Louis, and Arlington.

Five other states have similar laws or court action permitting assisted suicide: Washington, Oregon, California, Montana, and Vermont.

Also on election day, California voted to legalise the use of marijuana for recreational use.