Rural firefighters and aircraft from around the country continue to battle a massive blaze in a forestry block in Marlborough's Wairau Valley.

An out of control fire in Marlborough has engulfed about 1000 rugby fields of pine forest, making it the biggest fire in the region in 15 years.

The 1150-hectare fire has been burning in the Wairau Valley, west of Blenheim, since about 11.30am on Thursday.

Blooms of smoke over the Waihopai Valley are understood to have caused some people to leave their homes.

DEREK FLYNN/stuff.co.nz Helicopters from all around the country have been called in to Marlborough to deal with a large forest fire near the Wairau township.

Marlborough principal rural fire officer Richard McNamara said it was the biggest fire in Marlborough since the Boxing Days fires of 2000.

"This is a big fire and it's moving quickly. But although it's a dynamic situation we can assure residents in the upper Waihopai Valley that there's no direct threat to houses or buildings."

The fire was 'spotting', or throwing out embers, which were starting small fires, up to 700 metres from the fire's edges.

1 of 32 SCOTT HAMMOND / FAIRFAX NZ Comand centre day four of the Wairau Valley fire. Seven helicopters on standby. 2 of 32 SCOTT HAMMOND / FAIRFAX NZ This helicopter departs for a reconnaissance flight . 3 of 32 SCOTT HAMMOND / FAIRFAX NZ Lead pilot Own Dodson of Marlborough Helicopters takes a well deserved break. 4 of 32 SCOTT HAMMOND / FAIRFAX NZ Owner of the ZK-HUE Bell UH-1Iroquois. The helicopter can carry up to 1500 litres of water in monsoon bucket. 5 of 32 SCOTT HAMMOND / FAIRFAX NZ Incident controller Chris Hayles with air attack supervisor Paul Devlin. 6 of 32 SCOTT HAMMOND / FAIRFAX NZ Time out 7 of 32 SCOTT HAMMOND / FAIRFAX NZ Waihopai families supplied the firefighters with an abundance of food and drink. 8 of 32 SCOTT HAMMOND / FAIRFAX NZ Action Fire Management from Motueka unload from a helicopter after spending a 10 hour shift in the forest. Riki Te Moananui in front 9 of 32 RICKY WILSON Dry pasture in the Waihopai Valley. 10 of 32 SUPPLIED Smoke from the forest fire in Wairau Valley. 11 of 32 BEN HIDE Flames rip through forestry in the Wairau Valley, Marlborough 12 of 32 BEN HIDE Flames rip through forestry in the Wairau Valley, Marlborough. 13 of 32 DEREK FLYNN / FAIRFAX NZ Eleven helicopters with monsoon buckets were fighting the fire in Wairau Valley, Marlborough 14 of 32 DEREK FLYNN/FAIRFAX NZ A Helicopter returns to Omaka Airfield after battling a large forest fire in the Wairau Valley, Marlborough. 15 of 32 DEREK FLYNN / FAIRFAX NZ The fire in the Wairau Valley, Marlborough now covers about 1100ha 16 of 32 DEREK FLYNN / FAIRFAX NZ A Helicopter returns to Omaka Airfield after battling a large forest fire in the Wairau Valley, Marlborough. A thick plume of smoke hung over the region at sunset. 17 of 32 SUPPLIED Smoky sunset over the Wairau Valley in Marlborough 18 of 32 SUPPLIED Smoke could be seen throughout Marlborough as the forest fire rages in the Wairau Valley. 19 of 32 BEN HIDE Flames rip through forestry in the Wairau Valley, Marlborough. 20 of 32 BEN HIDE Wairau Valley forest fire 21 of 32 SUPPLIED Helicopters with monsoon buckets struggle to get the fire under control. 22 of 32 WENDY RUSSELL Farmers have been advised to get their stock out of the way of the raging blaze. 23 of 32 WENDY RUSSELL The forest fire is going to be a long, hard one for the firefighters. 24 of 32 WENDY RUSSELL Smoke from the forest fire in Wairau Valley captured a few kilometres away from the location. 25 of 32 SUPPLIED Forestry block buring in Wairau Valley. 26 of 32 SUPPLIED The sky is getting darker and the temperature is around 28 degrees in Marlborough. 27 of 32 SUPPLIED Smoke from the forestry fire in Wairau Valley, Marlborough. 28 of 32 BRENDON BURNS Smoke from the forest fire in Wairau Valley 29 of 32 SUPPLIED Smoke colours the sky in Marlborough 30 of 32 SUPPLIED Smoke billows into the sky above the Wairau Valley. 31 of 32 SUPPLIED Smoke from the forest fire seen from the Wairau Valley School. 32 of 32 SUPPLIED Smoke from the Wairau Valley fire can be seen from Landsowne Park in Blenheim.

The Boxing Day fires burnt through 7000ha of grassland on the edge of Blenheim.

"This fire is burning far more intensely and it has a hundred times the fuel loading in front of it compared with the light grassland on the Wither Hills, but fortunately it's well away from any settlement," McNamara said.

Two other large fires in Marlborough this year were smaller, with 600ha of pine forest lost at Onamalutu in February and 450ha in Waikakaho Valley two weeks ago.

Jennifer Eder Ground crews on site at the Wairau Valley fire in Marlborough

Saturday afternoon was expected to be a crucial period for firefighters, he said.

"We want to get as much control as possible before another hot norwester arrives."

About 15 aircraft were dispatched to fight the fire on Friday, including two large fixed-wing planes from north Canterbury with the capacity to dump two tonnes of water each.

One of the fixed-wing planes was sent back over concerns there were too many aircraft for the airspace.

Ground crews were being sent in to attack the less dangerous areas. It was previously too dangerous for crews to fight the fire from the ground.

Marlborough rural fire officer Chris Hayles said relatively calm conditions were giving ground crews a chance to battle the fire from the flank but the thick smoke was making it difficult for aircraft to take-off and land.

SUPPLIED The extent of damage from the Wairau Valley fire on Friday morning. Moderate winds have blown embers into the neighbouring Waihopai Valley and 'spotted', causing multiple small fires just over the ridge between the valleys.

A thick haze of cloud and smoke had settled over the valley, which only high temperatures or strong winds would move, causing visibility issues for aircraft, Hayles said.

The staging area for emergency crews, including the New Zealand fire service command unit, the Marlborough Civil Defence response unit, and a precautionary ambulance was moved a few paddocks north overnight as the fire front drew closer to the original staging site.

The fixed-wing plane and helicopters were sharing a paddock to load water from tankers.

It was a small take-off space to share, but if pilots kept in radio contact there should not be any incidents, Hayles said.

Marlborough Emergency Headquarter spokeswoman Karen Fisher said the fire had gone up the ridge and smoke was blowing over the Waihopai Valley.

"They've got machinery in there to try and carve some fire breaks," she said.

"They [firefighters on the ground] will be up there and around and so forth. The biggest problem yesterday was getting the water in."

Firefighters would be tackling the blaze "around the edges a little bit . . . but it's not a ground attack".

Fisher understood some Waihopai Valley families had left their homes overnight "because of the smoke".

The majority of the fire was burning through Nelson Forests production blocks but two private forestry blocks had also been affected.

On Thursday, authorities said the fire covered between 100 and 200 hectares, mostly over land belonging to Nelson Forests.

"It's not under control yet and it will be some time [before it is]," Fisher said.

Temperatures were expected to reach a high of 25 degrees Celsius in Blenheim on Friday and rain might develop in the evening.

The region's rural fire chief Richard McNamara said the weather conditions were much better than those which hampered containment efforts during the Waikakaho Valley fire two weeks ago.

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Rain was forecast for Saturday afternoon but Metservice advised on Friday that northwest gales could become severe in exposed parts of Marlborough on Saturday and Sunday.

Farmers in the Waihopai Valley were advised to exercise their own judgment and move stock as they felt necessary.

Key messages from Marlborough District Council:

Parson's Rd is closed at the intersection with SH63.

Speed restrictions of 30kmh are in place and motorists are asked to exercise caution and patience as water tankers are crossing the state highway.

The general public is asked to avoid the area if possible.

Anyone driving in rural Marlborough should be aware of the smoke and take extra care where visibility is restricted.

Farmers in the Waihopai Valley closest to the fire zone should exercise their own judgement and move stock if they considered that to be prudent.