Prime Minister John Key has visited some of the areas worst affected by the quake around Kaiapoi and Darfield.

A 5.1 magnitude aftershock – the strongest yet – struck just as the tour got underway.

Agriculture Minister David Carter was with the PM, and says the scale of the destruction is almost unbelievable.

“The size of this disaster is absolutely huge, different people we’ve met are responding with different abilities.

"Many farmers we’ve spoken to, some of them severely knocked around, are responding very quickly and pragmatically, they’re working efficiently to get back on their feet.

Mr Carter says residents will need all the support they can get in order to recover.

"We hope to be announcing a bit of a plan as to how we will co-ordinate a response from Government [soon].

"We still need to get a good feel for the extent of the damage, and once we have a fairly good grasp, the next question is ‘how much of that is insured?’ Because if it’s insured the insurance companies, along with the Earthquake Commission, will take care of those.”

Irrigation New Zealand is urging farmers to make thorough checks of their wells, pipelines and systems and to take extreme care as power supplies are restored.

INZ chairman Graeme Sutton says the damage to water supplies won’t be fully known until systems are turned back on, and farmers should make tests a priority even if they don’t need irrigation immediately.

“To go and turn your pump on and say ‘I’m irrigating today’ is not the right attitude.

"It may be that a more gentle approach with awareness of the potential damage is the way to approach this kind of testing.

Mr Sutton says ground disturbances may cause bores to supply more or less water, and farmers with specific concerns should seek technical support.

"We’re encouraging people to contact their supplier if they have any problems, but also to let us know so we can build up a database of where the problems seem to be most common.”

Anyone wishing to call the Federated Farmers earthquake helpline should ring 0800 FARMING, that’s 0800 327 646.