A second fire has broken out in the Tasman region, close to another fire which has already led to mass evacuations.
The new fire is on Rabbit Island, close to Pigeon Valley where the original fire started yesterday.
About 170 properties have been evacuated in the area, and the fire has been declared a Civil Defence emergency.
"This was extreme fire behaviour, there was no way we could stop this fire," a Fire and Emergency incident controller Ian Reade said.
Nelson Tasman Civil Defence said the growth of the fire had slowed because of lower temperatures and moisture in the air. But the situation could change quickly if temperatures rose and wind increased.
Firefighters were working on the ground in Evens Valley, Redwood Park and Pigeon Valley, and 16 helicopters were working to protect homes and manage the fire.
Some of those helicopters have been pulled away to deal with the new fire on Rabbit Island.
The fire began yesterday afternoon and was allegedly started by a farmer ploughing his field.
It was still out of control this morning and fire crews were hoping a wind change from southerly yesterday to northerly today would help slow the fire spread.
Tactics today included a "massive air attack", involving fixed-wing aircraft, and also heavy machinery on the ground to create fire breaks.
They did not yet know how many properties had been destroyed, but there were reports of damage.
The fire also came close to destroying the Eves Valley sawmill, but some "sterling work" kept that intact, Reade said.
They had no idea how the fire started, but believed it began outside of the forestry blocks.
A fire investigator was due to arrive this morning.
The New Zealand Defence Force had stepped in to assist providing a RNZAF C-130 to fly police and fire personnel from Wellington to Nelson, and three fire trucks and seven firefighters.
Police inspector Zane Hooper said people who have not been evacuated should make sure they have access to radio or cellphones that have the ability to receive messages and updates through mainstream media.
Anybody who was evacuated from the fire area needed to go to the evacuation centre at St John Anglican Church on Edwards St, and record their details there.
"This is a fast-moving situation," Hooper said.
Police had about a dozen staff working yesterday and overnight went door to door warning of areas being evacuated.
Nelson Tasman Civil Defence group controller Roger Ball said anybody evacuating should take essential items, including food, water, clothing, medicines and pets.
Tasman mayor Richard Kempthorne said at 8am they had declared a Civil Defence emergency.
The declaration gave authorities at work powers to "do things they need to do", Kempthorne said. This included allowing police to evacuate people quickly to protect them if necessary.
"It is a horrendous fire. It started yesterday afternoon and travelled really quickly.
"You always hear of fire, but to see it last night and experience it the way we did was amazing."
Kempthorne said he and Nelson mayor Rachel Reese were personally affected by the fire with property in the area.
"All they were able to do was leave, there was stock involved, that was the case for a lot of people."
He recommended affected people make their way to the welfare centre at the St John Anglican church, where volunteers were doing a "tremendous job" offering food and support.
"A lot of people have been rattled by this."
Despite the tinder-dry conditions they had "no expectation" fire could break out like it did.
"This is a well-run forest. This just shows the exposure we have when a fire breaks out."
"A week or two ago we started closing blocks of forest to the public, there is a lot of walking and mountain biking there, and some people thought, 'I am not going to light a fire, what is the risk?' Last night we saw the risk. It just takes off so quickly."
Kempthorn said it was a warning for areas around the country with forestry and experiencing dry conditions.
The fire that started yesterday afternoon in Pigeon Valley had doubled in size overnight and spread to cover 1870ha within a perimeter of 20km by 3am, a Fire and Emergency NZ spokesman said.
Civil Defence Minister Kris Faafoi says crews battling the fire have been given all the equipment they need.
He says additional aerial resources are on their way to the region to ensure if the blaze spreads any further they're in a position put it out as quickly as possible.
Fanned by southerly winds over most of the night the fire has caused material damage from Pigeon Valley north to the Inland Moutere Highway and Waimea West Rd.
People have been evacuated from Eves Valley, Golden Hills Rd, Redwood Valley Rd, Mallings Rd and Greenacres Rd.
Notices of potential evacuation are in place for top end of Sunrise Valley and Deep Dale Rd in Upper Moutere and Pigeon Valley.
There have been no reports of injury or worse.
If people evacuate and leave their homes it is asked they register with the Civil Defence Centre at St Johns Church, Edwards St in Wakefield and to ring Civil Defence, 03 5437290, to register they have moved and are safe. This is important to ensure everyone is accounted for and safe.
If people feel unsafe or unsure in any way, they are advised to self-evacuate to the Civil Defence Centre.
Auckland woman Sarah Dance landed in Nelson yesterday afternoon about to embark on a holiday in the region.
They were intending on heading to Kaiteriteri but given the conditions they were now planning on heading south to Blenheim.
She was still in Nelson this morning and noticed a smell of smoke in the air. Weather conditions had calmed down considerably, she said, with the wind abating and little drizzle scattering the area.
Stephen Cox said the Nelson area hasn't seen rain in over a month and with dry conditions the wind is helping to fuel the fire.
Cox said he first heard sirens shortly after 2pm yesterday and only a small plume of smoke could be seen. Now there was a "huge ball of smoke".
"[It has been burning] at least two and a half hours ... there was only a small amount of smoke but since then we've had multiple fire engines, multiple police vehicles all hurtling out there.
"We haven't had rain here for weeks and weeks and there's quite a strong southwesterly wind helping the blaze."
"There's just a huge ball of smoke and [water] tankers going out there and fire engines going out there."
Updates to the situation will be posted on the Tasman Marlborough Fire Area Facebook page.
Due to high temperatures, dry soil and vegetation, fire risk is extreme in Northland, Coromandel, Nelson, Marlborough. A total fire ban is in place for these areas.
Fire risk is also high and fire restrictions are in place in Auckland, Hawke's Bay, Bay of Plenty, Central North Island, Wairarapa, Southland/Otago and, as of January 29, North Christchurch.
If you are in one of these areas and thinking about lighting a fire, go to www.checkitsalright.nz to check your fire type and, if needed, apply for
The annual event means closures for some lanes on the city's harbour bridge.