NSW Rural Fire Service Inspector Ben Shepherd said a substantial number of emergency crews were called to Ardlethan Road at Cowabbie before midday after reports of a fire igniting in a paddock.

The fire burnt up to 450 hectares requiring 30 fire trucks and two water-bombing aircrafts to contain the fire by 1.45pm.

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It is believed the fire was caused by a header, however Mr Shepherd said they are unsure at this stage if the farmer suffered any crop loss.

Mr Shepherd urged farmers to continue monitoring conditions, check harvest safety alerts and when conditions become too risky, cease operation until they ease.

"Albeit, we have seen a number of harvest fires as a result of harvest operation over the last few weeks, but by-and-large we are seeing harvesters coming off the paddock during the worst times of the day and they are adhering to the safety alerts," he said.

"What we are seeing, especially in standing crops that each hectare lost for some of these farmers does equate to more than $1000.

"It can be a substantial economic loss and we don't want to see the fires or landholders losing that money especially after a number of years in drought."