A mercy-killing campaigner has demonstrated for the first time a prototype do-it-yourself suicide machine designed to kill quickly and peacefully with a few breaths of carbon monoxide.

The machine, a sealed container with some plastic piping and hoses, mixes two ingredients to produce carbon monoxide.

The deadly gas is delivered to the subject through a thin transparent plastic hose.

Dr Philip Nitschke, who developed the machine at a cost of AUS$10,000 (£4,000), said it was designed so people who wish to take their own life could build it at home for less than AUS$100 (£40).

He told a mercy-killing conference in Sydney, Australia that it would allow people to take control of the final stage of their lives.

"Ascetically it's troubling, but physiologically it's peaceful," said Nitschke, founder of the pro-euthanasia organisation Exit.

"Dying is a natural process like child bearing - you can do it yourself and you don't have to have a white coat and nurses standing alongside the bed," he said.

Outside the conference, members of the anti-euthanasia Right to Life movement demonstrated against Nitschke - who they have branded Dr Death - and his machine, which is simply called CO Generator, using the chemical symbol for carbon monoxide.

Exit, which has more than 3,000 members in Australia, runs workshops advising terminally ill people on how to commit suicide. The average age of members is 75.

Teams of Nitschke supporters will demonstrate how to make and use the CO Generator to workshops in Sydney, Melbourne and Brisbane in August.