A field trial of genetically modified pines near Rotorua has been broken into and 19 trees chopped down in an apparent protest.

The attack was condemned by some anti-GM groups, who said it could have caused the spread of contaminated material and harmed New Zealand's green image.

No group has claimed responsibility for the break-in, which happened over the weekend and was discovered at forestry research group Scion's Rotorua base on Monday morning.

Police found a 1.5 metre hole and a damaged section of fencing, which had allowed somebody to burrow underneath it.

A police spokesman said 19 small pine trees, each about 1.2 metres high, were cut down.

A spade with a "GE Free New Zealand" sticker on it was found beside the 3.5 metre high electrified fence.

But GE Free New Zealand national spokesman Jon Carapiet said that meant "nothing".

"Tens of thousands of people have those."

The field trial was installed in 2003 to look at the impact of genetically altered trees on the environment.

The trees were genetically modified to grow faster, produce better wood, and improve their resistance to pests and herbicides.

Two years ago anti-GM group People's Moratorium Enforcement Agency (PMEA) held a demonstration at the site, which resulted in the arrests of four people.

Nobody from that group could be contacted last night.

Other protests have targeted the planting of genetically modified crops.

The Green Party has described genetic engineering as "a gamble" with no control over whether the results will produce more than just the single effect that is usually wanted.

Mr Carapiet said the break-in was irresponsible, and could have spread GM material from the site, potentially harming New Zealand's image overseas.

"That is of extreme concern," he said.

Mr Carapiet's worries were shared by Soil and Health spokesman Steffan Browning.

He recently slammed the experiment as poorly run.

He said animals such as rabbits and cats were easily able to get inside and spread GM material around.

Mr Browning said Soil and Health did not condone illegal acts.

"But it is one less GE trial for the public to worry about."

Scion's acting chief executive, Elspeth MacRae, said it was confident no genetically modified material was moved outside the site during the break in.

"There are no concerns surrounding contamination."

She said the police, the Environmental Risk Management Authority, and the Agriculture and Forestry Ministry were investigating.

- © Fairfax NZ News