Australian wallabies are eating opium poppies and creating crop circles as they hop around "as high as a kite", a government official has said.

Lara Giddings, the attorney general for the island state of Tasmania, said the kangaroo-like marsupials were getting into poppy fields grown for medicine.

She was reporting to a parliamentary hearing on security for poppy crops.

Australia supplies about 50% of the world's legally-grown opium used to make morphine and other painkillers.

"The one interesting bit that I found recently in one of my briefs on the poppy industry was that we have a problem with wallabies entering poppy fields, getting as high as a kite and going around in circles," Lara Giddings told the hearing.

"Then they crash," she added. "We see crop circles in the poppy industry from wallabies that are high."

Rick Rockliff, a spokesman for poppy producer Tasmanian Alkaloids, said the wallaby incursions were not very common, but other animals had also been spotted in the poppy fields acting unusually.

"There have been many stories about sheep that have eaten some of the poppies after harvesting and they all walk around in circles," he added.

Retired Tasmanian poppy farmer Lyndley Chopping also said he had seen strange behaviour from wallabies in his fields.

"They would just come and eat some poppies and they would go away," he told ABC News.

"They'd come back again and they would do their circle work in the paddock."

Some people believe the mysterious circles that appear in fields in a number of countries are created by aliens. Others put them down to a human hoax.