Rewi said the exterior wallboards had been scorched.
Reverend Ruth Dewdney echoed Rewi's comments.
"We were very lucky we have a good smoke detection system and that the fire brigade is so close," she said.
She said smoke went into the Centennial Room and triggered the smoke alarm very quickly.
The initial belief was that the fire had been close to an air conditioning unit because that's where the smoke damage was, but there was also a burnt area on one of the window ledges.
With very little damage inside the church, and the building ventilated as far as was practical, Ruth was able to conduct a funeral service with 200 people in attendance later that morning and there was no disruption to Sunday worship.
"We had to disconnect one of the air conditioning units so it was a little warmer than usual," she said.
"We are very grateful to the fire brigade and to previous church management committees for their foresight in putting in a good smoke detection system."
Jon said it appeared the fire had been deliberately lit.
"There was nothing there that would have caused the fire.
"Scorched patterns on the wall indicated somebody had started the fire."
A police media spokeswoman said police were called to the scene after firefighters reported the blaze may have been deliberately lit.
"It looks as though inquiries are ongoing," the spokeswoman said.
At press time there had been no further developments in the investigation.
