"Now we have to plan what to do ... we can't just call and say 'don't come'. It's a big stress.''
Mr Nandan said the wedding ceremony was taking place beneath a canopy in the back garden when he heard what sounded like a gunshot ring out.
"Then we just saw the smoke and the fire and we couldn't do anything, we just tried to save ourselves first.
"I tried to go inside but I can't go ... it was a huge fire.''
No guests were injured but the house was destroyed. The fire also blistered paint and smashed a window of a neighbouring house as it was fanned by strong winds.
Mr Nandan said the house was rented by his parents, who had lived there for about seven years.
The bride was being comforted by family at her mother's house, he said.
Family friend Raj Prasad said the wedding party would gather at a nearby address where they would take stock of what had happened and plan their next move.
The family hoped that the wedding could still take place today or tomorrow, he said.
Firefighter Alexander Betteridge, of Papatoetoe Fire Station, said when they arrived just after 3pm it was too late to save the house.
"Flames were roaring out the window and licking on the paintwork on the house next door. It smashed the window and the flames almost got in but we managed to stop it.
"If we'd been another five or 10 minutes the house next door would have been going too.''
The cause of the blaze had not yet been established and was being investigated by a fire safety officer.
Police were also at the scene.