A large blaze at a Christchurch substation has now been put out by fire crews.

Residents heard explosions coming from the Islington substation, which is run by Transpower, and fire crews from across the city were called to the Roberts Rd address about 1.30pm.

Police closed Roberts Rd between Brunner St and Pound Rd.

1 of 6 Residents heard explosions. 2 of 6 JOHN FOE Flames were seen leaping from the substation. 3 of 6 SUPPLIED Thick, black smoke and flames, seen from a neighbour's garden. 4 of 6 SUPPLIED Black smoke billowing from the Islington Substation. 5 of 6 Kevin O'Kane / Facebook Firefighters are battling to contain the blaze. 6 of 6 Kevin O'Kane / Facebook Residents have been watching the drama unfold.

Fire Service spokesman Brent Dunn said it was an oil fire inside a secure area at the substation.

Seven crews from Addington, Harewood, Christchurch, Sockburn, Woolston and Rolleston attended.

While they were at the scene, firefighters were called to another fire on a rural property in West Melton about 2.50pm.

JOHN FOE Flames were seen leaping from the substation.

A large garage and barn fire were "well ablaze" on Halkett Rd, near Sandy Knolls Rd, Fire Service southern communications shift manager Brent Dunn said.

Back at the substation, Dunn said they were using foam to extinguish the blaze.

Islington resident Jenee Puller said she heard explosions come from the site.

KEVIN O'KANE/FACEBOOK Residents reported hearing explosions as a power substation caught fire on Monday.

"Just heard three loud bangs, looked outside and saw smoke and flames everywhere."

Puller called emergency services.

Neighbour Kate Cameron said "it sounded like gunshots."

LIZ THOMPSON The substation fire as seen from from central Christchurch.

A Transpower spokeswoman confirmed the fire was at the substation and staff were assisting fire crews.

She did not yet have details on the size of the blaze or what may have caused it.

The Fire Service had not been called in to investigate the cause of the fire and the site was handed back over to Transpower just after 4pm on Monday.