"There are big deep gullies and a lot of hot area in there. It spread very rapidly."
The fire is now under control and the helicopters have been stood down.
Fire crews are currently working on putting out little spot fires caused by embers.
Firefighters were fine for water supply, despite initial fears they would run short.
Fire crews would spend the rest of the day and overnight keeping an eye on hot spots.
A group of five teenagers who had been swimming at the AC Baths crossed the road to where the fire was to take a closer look.
They described it as being as big as two rugby fields, if not bigger.
They could hear the fire crackling in the trees.
"As the pine needles fell to the ground, they would start little fires on the ground," one of the teenagers said.
The teenagers told The Daily Post they were running around trying to stomp out the fires.
But the flames would spread quickly from one tree to the next.
The teenagers were later told to leave the area by emergency services staff.