The familiar silhouettes of the two 70-metre smaller stacks, the 140-metre tall stack plus the 55-metre water tower are no more after they were brought down with engineered and controlled explosive charges on Thursday morning.

The demolition and remediation works are part of Hydro's plan for the eventual sale of the 2000-site - which closed in 2014.

Hydro managing director Richard Brown said the demolition was an important "milestone" in reshaping the former smelter site for a brighter future.

"It's exciting. It's a significant milestone in the journey of the site from smelter to its future life," he said.

Plans for the 2000 hectare site include approximately 65 per cent of the land being set aside for conservation, 10 per cent for residential and industrial use (respectively) and 15 per cent for rural land.

Mr Brown said there were still several years of demolition and remediation ahead but the organisation was looking forward to the site's new life.

"This is part of the demolition phase, and the remediation phase is yet to come," he said.

"The majority of the site will be set aside for conservation such as bushland and wetlands.

"But we do hope that there will be some employment there in the future and a balance of outcomes, such as residential and industrial."

In its heyday, the smelter provided 1100 jobs, including many in the local area.

Kurri Kurri resident Wayne Cardow worked in the high voltage switch yard at the smelter from 1980 to 1981.

"It's sad day but it's the way things go," he said.

"I have some really good memories from working there.

"I went to Kurri Kurri High School, and we used to be able to see the stacks being built. Slowly, we saw it rise above the tree line until it stood at its full height. When you stood at the bottom and looked up, it was an awesome sight."

The next major part of the project, which is awaiting approval, will be construction of a fully engineered containment cell to hold demolition waste that can't be recycled.

Aberdare resident Gordon Foster, now 70, was just 17-years-old when he joined the crew building the stacks in 1966.

"I was pretty scared of heights when I first got the job but it went up seven foot six every day so you grew with it," he said.

"They were built in stages so I went back three times to work on each chimney. It's [the demolition] a milestone."

Mr Foster said he remembered when the crew attempted to paint the top of the largest stack but it "was that windy that we painted half the cars in the car park."

"It was funny if it wasn't your car," he said.

The site is now around 70 per cent demolished, with most of the three pot lines, the cast house and smaller structures also gone.

"The stacks fell just where we had planned. CMA Contracting has done a great job," Hydro Project Manager Andrew Walker said.

"CMA has been on site for two years now. We expect main demolition works to be complete by the middle of next year."