Demonstrators are due to march in Auckland, Wellington, Christchurch, New Plymouth and Dunedin against the lifting of the moratorium on the commercial growing of such organisms, mostly agricultural crops, at the end of October.

The marches, also planned in many smaller towns around the country, are a last-ditch attempt to persuade the government to extend the ban by at least a further five years.

Steve Abel, spokesman for environmental watchdog Greenpeace -- one of the groups joining the protests -- said the thousands turning up to march up Auckland's main street from noon were part of a "history-making event".

He said in a statement the aim was to send "a clear public message" to Prime Minister Helen Clark not to lift the moratorium.

Alannah Currie, spokeswoman for another participant, Mothers Against Genetic Engineering [Madge], said Clark had "got this issue wrong".

"There will be people there marching who have never marched in their lives, we will not go away, this is only going to get bigger," she told the New Zealand Herald Saturday.

New Zealand musicians Friday added their voice to the anti-GE message, donating songs to the Hang on Helen CD, which will be given away to people who send a "Hang on Helen" postcard to the Prime Minister.

Anti-GE protesters stripped naked outside Parliament this week, while Madge members turned up topless inside Parliament last month to protest against the lifting of the GE moratorium.

Some 69 percent of New Zealanders oppose the government's decision on the grounds that not enough is known about the long-term consequences of altering the genetic composition of plants, according to a recent Herald-Digi poll.

TERRA.WIRE