A MELBOURNE mum turned away from her 19-month-old son for only a short time, but it was long enough for the youngster to accidentally consume a fatal dose of liquid nicotine.

The child, who cannot be named for legal reasons, died in June 2018 after consuming the potent substance his mother had poured into bottles of vape juice as she tried to quit smoking, the Coroners Court was told on Monday.

She had turned around to put some of the bottles away at their northwestern suburban home before finding one of them open and in her child's mouth.

The woman washed the boy's mouth and called an ambulance but he died in hospital 11 days later from nicotine toxicity.

Coroner Phillip Byrne said it was not a case of neglect but a "momentary lapse of vigilance" by the mother.

He noted the child had been much loved and well cared for, and his family were shattered by his death.

Everything possible had been done to save the boy's life, Mr Byrne added.

The mother had imported the liquid nicotine from the US 18 months earlier and was mixing it with vape juice in an attempt to quit smoking.

Liquid nicotine, extracted from tobacco, is the fluid used in e-cigarettes.

The substance is classified as a dangerous poison in Australia and its sale is banned.

However, it is legal to import up to three months' worth of liquid nicotine for therapeutic use - such as quitting smoking - with a prescription (although laws vary state to state).

The inquest received submissions from health experts and the Commissioner for Children and Young People, including information about whether liquid nicotine should be legalised.

It has also heard from the Australian Tobacco Harm Reduction Association, which wants to see the ban on vaping nicotine overturned.

"I don't want to go down that path without further consideration," Mr Byrne said of the controversy surrounding the substance.

He will hand down his findings into the boy's death at a later date.

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