A fire that engulfed a Kaitaia church this morning is being treated as suspicious.

The incident occurred about 5.30am, Fire Service spokeswoman Megan Ruru said.

Two crews attended the blaze at the large site in central Kaitaia and the fire was well involved when they arrived, she said.

A fire investigator would head out to the scene at first light, she said.

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"It was 20 metres by 30 metres and our fire investigator will be going to investigate the cause.

"It's considered suspicious," Ms Ruru said.

The extent of the damage is not yet known.