The fire service have asked local residents to keep their windows and doors closed if there is thick smoke.
Meanwhile, South West Fire and Rescue Service said a wildfire was being tackled on Cowbridge Common, Vale of Glamorgan, on Wednesday.
Jones, who has been a shepherd for the Elan Valley Trust for 26 years, said the fire had created uncertainty and he will not know the financial impact until it has been put out.
“As a shepherd, I think about the stock,” he said, adding that he was concerned about lambs that had been on the hills “all winter”.
“It’s a big, big area. Big farms up this area. What are we talking, between 10,000 and 12,000 acres – could be more even, but it’s a job to say,” he said.
