A scrub fire has taken hold and is spreading, near Kawakawa in the Bay of Islands.

Four fire service trucks and a helicopter from the rural fire service are on their way to the blaze, on Ranui Rd in Karetu.

Northern Fire Communications shift manager Scott Osmond said they couldn't know how serious it was until they got there.

"The callers said it was grass and gorse on fire, and it's spreading.

"They said it was about the size of a couple of tennis courts, but it's spreading down a gully now."

More to come.

- NZ Herald