Explosions have demolished the main section of the Northern Power Station at Port Augusta — 18 months after Alinta Energy closed the coal-fired power station.

The two 80-metre tall boilers, containing 10,000 tonnes of steel each, were brought down by a series of explosive charges.

Contractor Andrew McMahon said the scale of the task was unprecedented.

"It's one of the biggest fellings undertaken in the world, certainly in the Southern Hemisphere," he said.

Locals watched the demolition from a safe distance. ( Supplied: McMahon Services )

Brad Williams from Flinders Power, the company responsible for the site, said wind conditions were perfect.

"Looking at it from a distance, it seemed to be perfectly executed, so we'll go into site shortly and look at it up close," he said.

The Port Augusta community has a strong connection to the former power station, which, along with the Playford A and B stations, was the city's largest employer until it closed in May 2016.

Local crowds gathered at vantage points around the fringes of the city to watch the explosion.

"It's a bit emotional," former worker John Miller said.

"I saw the place built, constructed and commissioned, so I thought, it's a whole thing for me, the life cycle, just to see it finally ended, I guess.

"Originally I wasn't going to come ... then I thought it's going to happen whether I'm there or not, so I'll go and watch it happen.

"It's been a sad moment, for sure."

It was the latest in a string of explosions and demolition works at Port Augusta's former coal-fired stations, with the site's decommission and remediation expected to be complete by mid-2018.

The coal mine at outback Leigh Creek, which fed the Port Augusta operation, closed in 2015.