UPDATED 6.43pm: A fire at a Christchurch powerstation has been put out, but the cause remains unknown.

Thick, black smoke could be spotted from across the city after the blaze began at the Islington station around 1.30 this afternoon.

A fire service spokesperson said it took about an hour and a half for the blaze to be fully extinguished.

There have been no reports of harm or injury to the public.

Investigators will be at the scene tomorrow. 

Earlier this afternoon, fire crews were brought in from throughout the city to help battle the blaze using foam.

The fire was called in by multiple members of the public at about 1.30pm, and there had been reports of an explosion.

Edward O’Driscoll saw black smoke billowing from the substation, as he was driving along Christchurch’s Main South Rd.

He said other witnesses had reported hearing an explosion.

11-year-old Brooklyn Morgan was at home when he saw the Islington substation go up in smoke.

"I was walking around inside, it sounded like gunshots. I heard bangs, and came outside, and could see smoke coming from across the road."

He did not see flames and said by about 2pm he could no longer see smoke in the area.