Federated Farmers is urging Canterbury farmers with quake-damaged grain silos to get expert advice before trying to empty them.
At last count, more than 50 silos had collapsed; dozens more are at risk of doing so.
A spokesperson for the federation's grain and seed section, John Hartnell, says the silos left standing by the quake are very weak, and farmers are worried the next heavy rainfall or strong wind will topple them.
Mr Hartnell says the federation is extremely concerned by poor advice circulating about how to empty damaged silos.
He says unstable silos weighing up to 120 tonnes are highly dangerous and farmers need to get them checked by an engineer or silo company representative before touching them, because failure to get proper advice could be fatal.
Mr Hartnell says workers have been putting in long hours getting the grain vacuumed up and moved to new silos.
He says most silos are carrying more grain than they usually would at this time of year because farmers have been reluctant to sell at the current low prices.