Three people, including two firefighters, have been injured at Alinta Energy's Northern Power Station outside Port Augusta after an explosion on Sunday morning.

The Country Fire Service (CFS) and Metropolitan Fire Service (MFS) were called to the power station about 11am where a fire had broken out in a coal deposit.

Crews were trying to prevent the fire from spreading to about 79 tons of coal within the property.

It was earlier reported four people were injured in the blaze, but South Australia Health confirmed it was just three.

One employee suffered burns to his face and hands and was flown to the Royal Adelaide Hospital.

Two firefighters were taken to the Port Augusta Hospital where one was admitted and one was later released.

A CFS spokesman said the cause of the blaze was still unknown.

An Alinta Energy spokeswoman said the fire had started in a coal bunker and sparked an explosion.

She said the incident was "now under control" but "a decision has been made to take the power station unit out of service" as a precaution.

"The appropriate authorities have been advised and the company will fully cooperate with their inquiries," she said.

The fire is not expected to cause disruptions to power supply.

Firefighters have used thermal imaging cameras to assist them.

The Northern Power Station sits alongside the Playford Power Station at the site.