Pigeon Valley fire continued to "burn actively" as it heads into its fifth day.
The blaze covers 2100ha with a perimeter of 27km.
Residents in Wai-iti, south of Wakefield, told: Prepare to evacuate.
Winds of 50km/h forecast in Nelson tomorrow, raising concerns the conditions could fan the flames.
With 22 helicopters battling the blazes, it is the largest aerial firefight on record.
It is also the largest forest fire since a blaze in Canterbury in 1955.
With firefighters still battling to get the Nelson bush fire under control, fears are that another 170 households comprising about 450 will have to evacuate.
Acting Tasman District Commander Inspector Zane Hooper tonight asked residents in Wai-iti, south of Wakefield, to be prepared to evacuate.
Whether or not they would have to leave their homes was dependent on the fire and the conditions through the evening and through the night.
"We will come knocking at your door if the situation demands that you leave," he said. "If you need to leave, you will need to leave quickly."
The movement of the fire would determine whether people would be told to head north or south.
About 1000 homes had already been evacuated with 2500-3000 people forced to hunker down with friends and family or head to shelters set up in the area.
Those who chose to self-evacuate, we asked to register their details with Civil Defence by calling the Tasman District Council on 03 543 8400, or visiting the Civil Defence Centre at Saxton Stadium.
Fears for tomorrow
With winds of 50km/h forecast in Nelson tomorrow, concerns are the conditions could fan the flames of the massive Pigeon Valley fire and prevent helicopters from flying.
The fire wreaking havoc near Nelson is burning into its fifth day, covering 2100ha with a perimeter of 27km.
Nelson-Tasman Civil Defence management controller Roger Ball said anything over 20 or 30km/h winds was pushing the fire over the control line.
Helicopters could fly in conditions of up to 50km/h winds, but they had to stop for safety reasons in winds above that, he said.
A declaration of emergency remained in place in Nelson today.
Ball told a press conference this afternoon that the situation remained "dynamic" with a risk to life, animals and property.
The cause of the fire was still under investigation by fire investigators and no arrests had been made, said a senior fire officer.
Ball said they could control, and contain this fire if they didn't get excessive winds and would do that in a matter of days, said Ball.
John Sutton, incident controller for the Pigeon Valley fire, said the focus was on two risky areas, including the northwestern area of the Pigeon Valley fire where the wind was currently coming from the northwest.
It was not currently posing a risk, but if the wind changed "there is a time bomb sitting there", he said.
There were currently 100 firefighters working on the fire with crew, including volunteers, being rotated to spend time with families and have a good sleep.
The control line around the parameter of the fire covered about 85 per cent of the area.
Mass evacuation
Just under 900 properties had been evacuated in the Wakefield area and about 200 properties in the Pigeon Valley area - a total of about 2500 to 3000 people.
Residents in the rural areas east of Wakefield who were outside the evacuation zone had managed access from 8am to 6pm today. The New Zealand Defence Force ran escorted convoys through the portion of SH6 that runs through Wakefield township. This allowed access through Wakefield for residents who would otherwise not be able to get past cordons on Eighty Eight Valley Rd, Totara Rd, Church Valley Rd and Bridge Valley Rd.
The highway remained closed for all other traffic.
"The escorted convoys will be running straight through the town with no stopping or diversions," a Civil Defence spokesman said.
"They is not an opportunity for residents within the evacuation zone to check on property."
Earlier in the week, 398 residents were evacuated from Pigeon Valley and one person has been hospitalised suffering from smoke inhalation.
"It is so dry and we are very vulnerable," said Tasman Mayor Richard Kempthorne, who urged the public to be vigilant.
"Just one spark can cause the next blaze."
Biggest fire in 64 years
The Pigeon Valley fire wreaking havoc has become New Zealand's largest forest fire in 64 years.
Fire scientist Grant Pearce said the Pigeon Valley fire was one of New Zealand's four biggest forest fires and similar in size to the Hira fire of 1981 that burned 1972ha close to Nelson City.
The largest forest fire on record was in 1946 when more than 30,000ha burned in the central North Island near Taupo, including 11,000ha of pine plantations. The next biggest was at Balmoral, Canterbury in 1955 when 3152ha burned.
Pearce, of the Scion Rural Fire Research Group, said New Zealand had also experienced a number of large grassland and scrub fires, including the Ohinewairua fire in the central North Island in 1983 that wiped out 15,000ha of tussock and beech forest.
Pearce said the fires were relatively small in international terms. Some wildfires in the Australian states of Victoria and New South Wales exceeded 100,000ha.
The current wildfires in Tasmania have burned more than 30,000ha.
Residents flee
Close call
"On Wednesday morning, we were honestly under the impression our house had gone."
Diarmuid Brazendale nearly lost his house to the blaze in Redwood Valley on Tuesday.
But they were safe, which was the most important thing, he said.
Countless numbers of friends had offered to take their family in, he said.
Tight-knit village split up
It's been almost 24 hours since Amby Cowe packed up her three young children and evacuated their Wakefield home, among hundreds of people evacuated as the devastating Tasman district wildfires continue to rage south of Nelson.
But as she holds her youngest, 18-month-old Fergus, she says she isn't worried about her own home.
"It's not the fire that's worrying me. It's our little village - it's all split up."
After earlier evacuations of rural residents in valleys including Pigeon, Redwood and Teapot, the emergency grew yesterday when it was decided the settlement of Wakefield, home to 3000, was at risk and would be evacuated in stages.
Residents from 860 homes were among those told to leave yesterday. Cowe and her kids left their Pitfure Rd home about 2pm, before a compulsory evacuation.
As Cowe gathered with more than 100 others at a public meeting in Appleby School this morning, the 37-year-old could see her local dairy owner, and her daughters' Wakefield School friends.
And she hoped the community would soon be reunited.
"We're feeling a bit displaced. We're feeling a bit strange without our village. We're a very tight-knit community and it's just strange to be away from all those close friends. We're all over the place."
In the meantime Cowe, her husband Matt and their kids are staying with Cowe's parents in Upper Moutere.
Little Fergus was unperturbed by the expected visit with grandma and granddad, but his older sisters, 7-year-old Shelby and 10-year-old Jody, were finding it a bit tougher, Cowe said.
"[We're treating it] like a bit of an adventure. We're just reassuring them. We've told them the emergency services need to get us out of the area so they can drop water on our house."
As for herself, the experience was more stressful than scary - there were some big decisions to make in a short amount of time.
"Not knowing when to leave, what to take? Do we pack in preparation for losing the house, or for just going out for a night?"
Seven-year-old family cat Tink couldn't be found, but she was confident the independent moggy would be able to feed herself on mice and would steer clear of danger.
The family couldn't take their fish tanks, and Cowe made the decision not to take too many things. Clothes for a couple of days, food and hard drives of photos were the main priorities.
That was a deliberate decision, she said.
"Nothing overly sentimental. I felt that if I started looking around I would just get more and more things."
The mail gets through The mail arrived for Redwood Valley evacuee Sally Kelly today - and with it some good news.
"Four days' worth of mail and no bills - so that's good."
Kelly is among thousands of Tasman district residents forced to leave their homes as wildfires south of Nelson enter their fifth day, and she was among those given their mail by NZ Post at a public meeting in Appleby this morning.
Her home in Red Stag Lane is safe, and Kelly is confident it will remain so, but she's looking forward to again sleeping in her own bed.
"It would be really nice just to be able to go home. I do understand everything, but it's starting to wear a bit thin now. We've been out since Tuesday, it's now Saturday."
Kelly, her husband, their Belgian Shepherd dog Mana and three cats are staying with family in Ruby Bay, but the couple had to leave their 14 sheep behind. She had been told the sheep had water, and also that they were fed last night.
"[That's good] because there's nothing in the paddocks."
She described most of the official response to the fires as fantastic, but communication had been patchy.
They had almost missed an escorted visit to evacuated properties, happening upon it by chance, because no one told them, Kelly said.
"I know Wakefield overtook everything yesterday and I know they're all still co-ordinating but it would be a help to get a bit more ... co-ordination and communication."
Support crew for firefighters
Wakefield resident Shelley Sims dropped everything to help with support on the home front as wildfires south of Nelson blazed.
On Wednesday, Sims found herself urgently packing lunches for the firefighters who would be spending hours in the air tackling the blaze from above.
Sims is a wholesale specialist at FreshBake in Brightwater.
There was a lack of staff rostered on in the bakery because it was a statutory holiday, and they needed to complete the work within a 50-minute window, she said.
"So I grabbed a customer who took their jacket off, washed their hands, and went out the back and started wrapping stuff.
"We couldn't have done it without him, 100 per cent."
Sims would find herself with another helper yesterday as her 6-year-old daughter was unable to attend school.
About 7pm she told the Herald her family was preparing to leave their home on Hooper Place, and it seemed like they were among the last to go in their area.
There were lots of helicopters and small planes flying over ahead. Sims likened it to a "war zone".
About 120 police assisted with the initial evacuation in Wakefield.
Earthquakes, now fire Justine Sharp has already lived through earthquakes in Christchurch and Wellington but described what unfolded as a being like something out of M*A*S*H*.