When Shilo Cullen saw smoke coming from the back of St John's Church, his first thought was for anyone inside.
As he rushed towards the building and yelled at the top of his lungs in case anyone was inside, the fire took hold.
Mr Cullen said it was shocking how quickly the fire engulfed the building.
He said when he first spotted the fire it was "a little bit of smoke coming out the back" but within a matter of minutes it spread.
"It was my first instinct to go and see if anyone was in there. I yelled at the top of my lungs and tried to listen if people were shouting," he said.
"It's the first time I've experienced such a massive fire. I don't think Rotorua has seen a fire like this for years.
"It was crazy how fast it went up."
He described the heat coming off the inferno as "unbearable" and the noise as a "roaring".
"Even when we were 100m away you could still feel the heat. It just kept getting hotter and hotter."
Mr Cullen said when the church went up in flames he quickly moved his car, which he'd parked next to it, then tried to phone emergency services.
Mr Cullen, who lives nearby, said he also alerted some neighbours in case the fire spread.
Driving past this morning he said he was surprised at the amount of damage.
Mr Cullen said his heart went out to those involved with the church and the families that used it.