Several vehicles were parked in the paddock belonging to farmers who had attended a stock sale at the yards yesterday morning. Mr Flowerday said the caretaker of the saleyards was the last person inside the buildings. Power was cut to make the area safe for fire crews.
"It was well involved in fire when we got here and at this stage we don't know the cause, so we're getting a fire investigator over here. There was power, so that is a possibility.
"We had a little fire spread to the neighbouring fence because of radiant heat but our first priority was to check for people or life, and then to stop any exposure fires, and that's where we directed our attack, to stop it spreading any further.
"Almost all of the equipment inside the structure was destroyed and most of the framing timbers were gone as well. But we did manage to keep it contained to the shed."
Masterton farmer Carolyn Powell was at a stock sale that had been held at the yards earlier in the morning and said sale agents had called an early stop just before smoke was seen rising from the nearby shed.
"There was a small sale and they had stopped for an early lunch or late morning tea and some of the agents started to leave and must have seen smoke, or flames.
"The rest of us started coming out to have a look and by that time flames were shooting out everywhere, so we rushed down and moved our vehicles."
The shed was a storeroom for tools, equipment and firewood, she said.