A girl killed by a brown snake in Far North NSW did not know she had been bitten until several hours later when she was almost comatose, the shire's deputy mayor says.

The six-year-old girl died on Saturday after being bitten on a property outside Walgett on Friday, prompting emergency services to issue a state-wide warning.

She was taken to Walgett Hospital, where doctors administered anti-venom, about 3pm on Friday.

She was then flown to the Sydney Children's Hospital in Randwick, where she was placed on life support.

After her condition deteriorated significantly, she was transferred back to Walgett Hospital, where she died.