Almost 30 firecrews - some from as far away as Yeovil and Warminster - have been fighting a major fire in Dorset overnight.
Crews from Sturminster Newton, Blandford, Shaftesbury, Sherborne and Beaminster were also called to the scene in Wareham.
Around 100 hectares of heath and woodland caught alight, in what was declared a major incident overnight involving 150 firefighters.
The cause of the fire remains under investigation.
Dorset and Wiltshire Fire Service say they expect the incident to continue throughout today with the A35 likely to remain closed for a number of hours.
People are being urged to avoid the area and local residents should keep their windows and doors closed.
A spokesperson for the Dorset and Wiltshire Fire Service said: "The A35 between Bere Regis and Morden Park Corner as well as Sugar Hill and Bere Road have been closed due to the smoke plume affecting a wide area and making them impassable.
"The smoke is being blown towards the Bournemouth, Poole, Ferndown and Wimborne areas.
"Residents are being urged to keep windows and doors closed as a precaution, particularly if you are experiencing coronavirus symptoms.
"Local people are also being made aware that due to the electricity pylons in the forest being affected by the fire, there may be some disruption to supplies in the local area.
"Residents should use the 105 service if they experience a power cut.
"At this stage, the cause of the fire remains under investigation, but with the Amber Wildfire Alert still in place, Dorset and Wiltshire Fire and Rescue Service would like to remind the public about the importance of staying fire-aware when out and about in the countryside."
Over 150 #firefighters now tackling the fire in #Wareham forest. Approx 100 hectares of heath & woodland affected & flames being fanned by strong winds. Smoke is drifting towards #Wimborne #Poole #Hamworthy If you’re worried about the smoke, stay indoors & keep windows closed. pic.twitter.com/GpNzbHiH6e— Dorset&Wiltshire FRS (@DWFireRescue) May 18, 2020
Today the Bournemouth crew have been assisting @DWFireRescue and @dorsetpolice with a large fire in #Wareham @WildfireTacAd was given an aerial view of the scene to help with the fire fighting strategy. This is an ongoing incident so please help by staying away. ^SM 🔥🚒🚁 pic.twitter.com/DBC74piQSc— NPAS South West Region (@NPASSouthWest) May 18, 2020
Assisting #Police #Patrol, @NPASSouthWest and @DWFireControl with a large #fire in #WarehamForest. #BereRoad is closed. #MarineCrimeCop is initial Police Incident Commander. #Dave5417 is assisting transporting colleagues. Follow #DWFire and @PurbeckPolice for updates. #Teamwork pic.twitter.com/vLOfx5fxq8— Dorset Marine Policing Team (@DorsetMarine) May 18, 2020
As our boat was out on a service call earlier, this picture was taken showing the huge smoke cloud from the devastating fire at Wareham. Stay safe to all emergency workers involved. @DWFireRescue @DorsetMarine @dorsetpolice @NPASSouthWest @DWFireControl @Bournemouthecho pic.twitter.com/UaYvm6wPZg— RNLI Poole Lifeboats (@PooleLifeboats) May 18, 2020
#TravelDorsetAlert: A35 around Bloxworth will likely remain closed overnight whilst firefighters continue fighting the large blaze at Wareham Forest, which has now been declared a major incident.— Travel Dorset (@TravelDorset) May 18, 2020
Please avoid Sugar Hill area around #Wareham forest as there is a significant fire ongoing with lots of smoke. We currently have multiple crews in attendance. Another reminder that our heaths are so vulnerable at the moment. pic.twitter.com/YwnXXV2TKh— Dorset&Wiltshire FRS (@DWFireRescue) May 18, 2020