An Australian teenager is in a critical condition after he was bitten by an inland taipan, one of the world's most venomous snakes.

The 17-year-old reportedly walked into Kurri Kurri hospital, north of Sydney, with the snake in a tub, after being bitten on his left hand.

It is not yet known how he came across the snake, which was more than 1,000 kilometres from its natural habitat.

"We were shocked. We've never seen a taipan before. They're not from this area and to have somebody bitten by an inland taipan is quite serious," said Judy Martin, a local reptile rescuer.

With one drop of the taipan's venom able to kill 100 men, Martin added: "He needs to take out a lottery ticket. He is extremely lucky to still be alive."