A newborn has died and another has suspected brain damage after nitrous oxide, also known as laughing gas, was incorrectly administered instead of oxygen at Bankstown-Lidcombe Hospital in Sydney's south-west.

New South Wales Health Minister Jillian Skinner said in a statement a machine in the neo-natal resuscitation unit had been incorrectly installed.

The incidents occurred this month and last month.

The mother of the baby who died, Sonya Ghanem, told Channel Nine coming home without her baby was devastating.

"I held my baby. They brang (sic) him to me at the hospital.

"I said 'I want to see him.'

"(I was) just looking at him ... shaking. My son 'wake up' I would tell him. 'Wake up, wake up. What did they do to you?'

"I come (sic) home to his room. No baby. No baby.

"Me walking, coming out of the hospital holding a capsule.

"I held nothing in my hand. I came empty-handed. Thinking I'd hold my newborn but no. Shocking, shocking this hospital," she said.

Ms Skinner said she was "profoundly sorry" and the operating theatre in question had been corrected but remained closed.

"I deeply regret these families have suffered through such a devastating error," she said.

"NSW Health will do all it can to support them."

Ms Skinner said hospital staff met with the families over the past weekend for "open disclosure" of the facts.

According to the Minister, the error was discovered last week when a paediatrician raised concerns following the death of one of the babies.

Hospital management is certain no other babies received gas from the affected outlet, she added.

Ms Skinner said the oxygen outlet was incorrectly installed by BOC Limited in July 2015 and the Government had contacted the company "demanding urgent advice" on how it occurred.

Gas company to conduct internal investigation

In a statement, BOC said it was saddened by incident and it was important "to identify the exact cause of this tragedy".

"We deeply regret that these families are suffering pain and sorrow," it said.

"As soon as BOC was notified of the situation we cooperated fully with all investigations being undertaken by the NSW Government - the hospital, the NSW coroner, and the Ministry of Health teams."

BOC added it was also conducting its own internal investigation.

Government must launch independent investigation: Labor

The Minister also said she had sought urgent advice on how the error happened and whether hospital staff followed protocols.

She also said every medical gas outlet in a NSW Health facility installed since the Liberal Government came to power in 2011 would be checked.

The Opposition's health spokesman Walt Secord said Ms Skinner must launch an independent review.

"This is every parent's nightmare, [it's] absolutely distressing," Mr Secord said.

"This is why the Health Minister must launch an immediate external investigation.

"There's no point the Department of Health investigating itself.

"Once it's investigated I want to see that after the families are consulted, that report is released publicly."