He could not recall any others at the island and in his opinion, "it would have to have been deliberately lit".
He had not yet been to the island to see the extent of the damage.
The island is a former pā site and has been an urupā "for generations".
"It is getting close to full, most people buried there now are in vaults."
Renowned Ngāti Ranginui leaders buried at the island west of the CBD in recent years include Wiparata Ngatoko and Dr Morehu Ngatoko Rahipere.
A Fire and Emergency New Zealand spokeswoman said "a lot of calls" came in about the blaze.
"We had to wait for a boat to transfer one appliance to the vegetation fire. We can't just drive over there. Some firefighters were wading over."
A helicopter was put on standby.
Mandie Thompson was driving along Takitimu Drive when she first saw the fire about 5pm.
She was "gobsmacked" by how quickly it grew.
"You could just see pillars of smoke coming up from the island and as we got further around along the expressway, you could see flames."
A funeral procession walks to Motuopae Island in 2013. Photo / FileShe witnessed the response for the next hour, while she waited for son's karate class to finish nearby.
First responders formed a line and passed along buckets of water to the island she said.
"The flames were huge and they were probably halfway across the island, but they managed to get it under control. It was a massive team effort."
Thompson grew up in Judea nearby and had always known the island was sacred land, so it was "devastating" to see it burning, she said.
A police spokesman said inquiries regarding the fire were "ongoing".
