Greenpeace protesters have broken into a CSIRO experimental farm in Canberra to destroy a crop of genetically modified wheat.

In the early hours of this morning a group of Greenpeace protesters scaled the fence of the CSIRO experimental station at Ginninderra in the capital's north.

Greenpeace says activists were wearing Hazmat protective clothing and were equipped with weed string trimmers.

They say the entire crop of genetically modified wheat has been destroyed.

About half a hectare of GM wheat is being grown on the site, as part of Australia's first outdoor trials.

No genetically modified wheat strain had ever been approved for cropping in Australia before.

Last month the CSIRO received permission to conduct Australia's first trial in which humans will eat GM wheat.

The wheat's genes have been modified to lower the glycemic index and increase fibre to create a product which will improve bowel health and increase nutritional value.

Animal feeding trials of up to three months have been conducted, with human trials at least six months away.

Greenpeace says it has taken action because of concerns over health, cross-contamination and the secrecy surrounding the experiments.

Campaigner Laura Kelly says the Federal Government needs to put an end to testing GM wheat in Australia.

She says parts of the United States and many countries throughout Europe have already rejected the crop, and Australia should do the same.

"No one is looking after the health of Australians. Julia Gillard isn't standing up to foreign GM countries to protect our daily bread so Greenpeace has to," she said.

CSIRO chief director of Plant Industries Jeremy Burdon says the organisation is still assessing the extent of the damage.

He says it is a setback to an important global food security program.

"Until we actually know what the assessment comes out at it's hard to say but if it sets it back by a year it's a significant amount of effort by those people involved," he said.

ACT Greens MLA Shane Rattenbury used to work for Greenpeace and says he is not surprised the group has taken such action.

"It's always very controversial these sorts of actions, but you have to stand up for what you believe in sometimes," he said.

"Greenpeace has clearly formed a view that the best way to both draw attention to this issue and to potentially protect the human food chain in Australia is to take this action."

Mr Rattenbury says Greenpeace has a track record of breaking the law to highlight problems.

"I've certainly been involved in action in the past where Greenpeace has broken the law and that has been necessary to highlight what we've considered at the time to be a greater issue than perhaps a simple trespass," he said.

ACT police have confirmed they are investigating but have not released any further information.