Factory workers in Melbourne's south-east got a shock when they discovered a white-lipped green tree viper on top of a box of plumbing supplies.

The venomous snake is thought to have crawled out of a box at the Dandenong factory which had come from Thailand.

Staff then called in snake handler Raymond Hoser to remove it.

"They had no idea what it was," he said.

"I drove to the factory expecting it to be a normal copperhead or whatever's native to the area and it turned out to be one of these tree vipers instead which is certainly a surprise.

"The only reason they found it in the factory is it actually crawled out of the box that it'd come in," he said.

Mr Hoser said he had never seen one of these snakes in Australia.

"They are dangerously venomous. There's no antivenom in Australia," he said.

"It's treated as dangerous, it would make you very sick but you'd be very unlucky to die from [a bite]."

Mr Hoser said despite Australia's tight biosecurity controls, snakes are small and can slide into tiny areas.

"It was very aggressive when I picked it up but it had some sticky tape attached to it," he said.

"Because I ripped the tape off the snake, it was very snotty and quite aggro.

"When I shifted it from a large container to a smaller container and an hour later, the snake was very placid."

The snake will be handed over to biosecurity officials.