Police and emergency services were called to the Big4 caravan park on Nailor Street in Hay at about 12pm on Monday.

Murrumbidgee Police District Acting Inspector Andrew Papallo said a cleaner and a worker, females aged 34 and 43, entered one of the cabins and "while they were cleaning came across an unknown substance and became ill".

"They have since been taken to Hay and Griffith hospitals, where they were treated and made a full recovery. They were released from hospital [Tuesday] morning," he said.

"We have some specialist police coming in from Sydney to do some testing and some cleaning. We still don't know what the substance was."

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Inspector Papallo said police were still investigating who was previously staying in the cabin and who might have left powder in "various areas" around their accommodation before the cleaners entered.

Fire and Rescue NSW also deployed 11 firefighters from Hay and Leeton to the incident site.

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