The explosion in a coal bunker occurred shortly before 11am yesterday, sparking a fire on the fifth floor of the power station.

A 24-year-old power station employee was airlifted to Royal Adelaide hospital for treatment of burns to his face and hands and is reportedly in a stable condition.

Firefighters were working yesterday to prevent almost 80 tonnes of coal adjacent to the power plant from igniting, however two firefighters sustained minor injuries while tackling the blaze and were being treated at Port Augusta hospital overnight.

So far the cause of the explosion has not been ascertained, but police and fire investigators were at the scene on yesterday.

The incident is now under control, but the power station unit has been taken out of service as a precaution.

The fire is not expected to cause disruptions to power supply in SA, and the adjacent Playford Power Station is unaffected.

The 240MW Playford and 544MW Northern plants were commissioned in 1963 and 1985 respectively to provide intermediate and baseload power for SA using coal sourced from the Leigh Creek coal field.

Between 2012 and 2014 the Northern plant's role was confined to the summer months while refurbishments were completed during the winter.

Since October the Northern Power Station returned to normal operation.

With the exhaustion of the Leigh Creek coal field expected by 2017 Alinta had examined other options for the plants, including gas-fired power, a $200 million solar option and nuclear power, but in 2013 a new low-grade blended coal deposit was identified that could sustain the plants until 2030.

Alinta claims the Northern Power Station is the lowest conventional marginal cost electricity generator in the state.

It emits around 3.6 million tonnes of greenhouse gases per annum.

Alinta is the largest private employer in both the Port Augusta and Leigh Creek communities with 200 direct staff and hundreds of contractors.