Firefighters monitor site of Mahurangi East fire believed to be caused by fireworks

Firefighters are still at one of the 40 or so blazes across the country started by New Year's fireworks.

A crew has been monitoring the site of a scrub fire at Mahurangi East in Auckland overnight.

The fire was the most serious in the North Island on New Year's Eve, breaking about 11pm on 31 December.

Fire and Emergency said six crews worked to keep the blaze from reaching nearby homes.

Inquiries continue into the cause of two large blazes in Te Waipounamu, the South Island.

In Dalefield, at Queenstown, neighbours claim a fire was started by millionaire Tony Malkin's private fire works display - although the origin of the fire is still under investigation.

A fire investigator is also on site in Marahau, in the Tasman region, where a fire on difficult terrain had nine crews fighting it at its peak.

Meanwhile, Southland firefighters are urging people to think twice about mowing the lawns when it is dry.

One spark from a ride-on lawnmower blade hitting a stone started a fire that could have cost a farmer their home in Southland yesterday, Fire and Emergency said.

Southland group manager Timo Bierlin said six crews raced to stop the fire from reaching the Wendon farmhouse, sheds, farm implements, and fuel supplies.

"It was a really close thing - the paint on the side of the house was bubbling and the guttering was destroyed," he said.

"We are really grateful to the volunteer firefighters who left their holiday activities to fight this fire."

The Waikaka, Waikaia, Riversdale and Balfour Volunteer Fire Brigades all attended, with one crew remaining on site into the evening to ensure there were no flare-ups.

Bierlin reminded people that dry grass easily caught fire.

With no significant rain forecast until at least the end of the week, he urged people to think twice about activities that could generate a spark.

"If you must mow, it's best to do so in the early morning when the day is at its coolest."