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On tractors and armed with packed lunches and shovels, volunteers are flooding into Christchurch from around the country to help.

They include hundreds of farmers from around the region - described by Christchurch Mayor Bob Parker as "the farmy army" - who were helping to clean up and distribute much-needed supplies to residents of stricken areas.

Federated Farmers president Don Nicolson said farmers had a lot to offer.

"Farmers not only bring labour but a set of skills built up over a lifetime and it's great that they have banded together to help out fellow Kiwis in a time of horrific tragedy."

Sam Johnson, who founded the thousands-strong Student Volunteer Army, said offers of support were pouring in from everywhere.

"At the moment we're getting bus-loads of people coming up from Ashburton and offers from everywhere in the country for volunteers to come down.

"There's been large numbers of farmers coming up with tractors and diggers and heavy machinery."

The group had received donations from other regions, including a truckload of bacon from Wellington and 500 packed lunches.

Mr Johnson said because the group was a "massive organisation", co-ordinators were trying to pinpoint the right areas to work through as methodically as possible.

He warned non-local volunteers that places to stay were scarce.

Individuals were helping out where they could, too.

Nelson doctor Bev Nicolls was in Christchurch to pick up friends from Britain who had been staying in the cordoned area of the city and could not get transport out.

He packed dozens of bottles of water into his car before driving down.

"If you're in Nelson you think, what can you do? By the time you've listened for two or three days, you've got a bit of a sense of what's happening.

"I just about bought out one of the Shell stations in Richmond and went in to Pak'n Save and got two-thirds of their packs as well."

Mr Nicolls also took down full petrol containers to fill up his car for the trip back.

"I didn't want to be queuing for ages and nicking fuel that someone else could have when I can get it freely up there."