By Phil Mercer BBC correspondent in Sydney

Voluntary euthanasia campaigners in Australia are preparing to distribute specially-designed plastic bags to help terminally ill people take their own lives.

The bags have an elasticised opening to provide an airtight seal around the neck, suffocating users, who take a sleeping tablet beforehand.

Proponents believe the bags will provide a way for elderly people suffering terminal illnesses to end their lives peacefully.

Critics have called on the Australian authorities to launch an immediate inquiry.

'Exit bag'

The "Aussie Exit Bag" has been commissioned by the veteran campaigner Doctor Philip Nitschke.

Dr Nitschke with the suicide bag

Speaking at the launch in Brisbane, Dr Nitschke said he will take delivery of 150 bags and distributed them free of charge to long-term members of the pro-euthanasia group Exit.

The bag allows users to take a sleeping pill while a cord automatically closes around their neck. Death, according to Dr Nitschke, would be neither violent nor traumatic.

He said that in the absence of voluntary euthanasia laws, the kits provided the only option for people lacking the money or connections to kill themselves with drugs.

Newspaper reports in Australia have said a terminally ill patient in Adelaide used one of the devices to commit suicide earlier this month.

The woman had said she could no longer bear her "horrific, pain-ridden existence".

Right to Life groups have demanded an immediate investigation. Peter Beattie, the Premier of Queensland, where the bags are made, has said he would be seeking advice on whether they were legal.

Euthanasia is banned throughout Australia, as is assisting suicide.

But Dr Nitschke has insisted the distribution of the bags did not amount to breaking the law.

For a brief period in the mid 1990s, mercy killings were legalised in Australia's Northern Territory before the intervention of federal authorities.

Four terminally ill patients committed suicide by lethal injection with the help of Dr Nitschke.