Two bonfires were lit by holidaymakers close to "total fire ban" notices on Uretiti Beach hours after a large scrub fire about 20km away threatened properties and cut power to 30,000 homes.

Firefighters from Ruakaka were cleaning their equipment and gear after returning from a scrub fire at Springfield, south of Whangarei Harbour, when they were called to the bonfires about 10pm on Sunday.

Ruakaka Fire Brigade station officer Jeff D'Ath was at pains to reiterate earlier warnings that there was a total fire ban in Northland.

About 50 people, mostly friends, lit the bonfires which were seen by fishermen who called emergency services.

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"The problem with those two bonfires was there was a total fire ban and signs written in plain English were up in the area," Mr D'Ath said.

"All it takes is a little breeze for the embers to shoot on the sandhills and threaten properties, including a large number of campers close by."

Mr D'Ath said those lighting bonfires thought they were safe just because they were about 20m from the sandhills and below the high water mark.

He said they were warned but that action would be taken if they lit fires in a public place again.

The group was asked to put the fires out in the presence of firefighters and police.

"Normally people would cover those fires with sand but the problem with that is the next morning kids would be out on the beach and could burn their feet," he said.

Mr D'Ath said like Northlanders, visitors to the region should familiarise themselves with fire risks because they risked being fined $1000 for lighting fires in a public place.

If fires they light got out of control, he said they could end up paying the charges associated with putting them out.

Ruakaka firefighters, he said, were still fielding calls from people who wanted to light open fires despite them being aware of a total fire ban in Northland.

Meanwhile, an investigation into the scrub fire at Springfield is expected to start today.

The fire started about 4.30pm on Sunday under the main Northland power transmission lines and burnt between 3 and 4ha.

Power was fully restored by about 8pm on Sunday.

Nearly 50 firefighters from 12 fire engines and three helicopters brought the fire under control about 7.30pm on Sunday and rural firefighters and crews from Forest Protection Services were mopping up yesterday.

Deputy principal rural fire officer for Whangarei and Kaipara Mike Sullivan said crews would be on the ground at least until tonight as there was still a bit of smoke and hotspots.

He confirmed an investigation into the cause of the blaze was expected to begin today.

Mr Sullivan repeated earlier advice for people to be careful around any form of ignition because the whole of Northland was still very dry.