The smell of smoke from a wood chippings blaze near Barnsley has drifted some 20 miles and can now be detected as far away as Sheffield city centre and Dronfield.
It is coming from a blaze at Crow Edge.
Staff at R Plevin and Sons reported the fire at their depot, which recycles wood and turns it into products including biomass pellets, at 8.10am on Monday.
Firefighters are still at the scene this morning and said the fire involves a pile of chippings measuring half the size of a football pitch and 20 metres high.
Residents living close to the site have been advised to keep their doors and windows closed.
An R Plevin & Sons spokeswoman said: “The isolated pile is currently being dampened down by South Yorkshire Fire and Rescue, which is creating steam and smoke.
“The Environment Agency have been made aware and we expect the situation to be fully resolved shortly.
“We will be working closely with the Environment Agency and South Yorkshire Fire and Rescue to readdress preventative measures to minimise the chances of this happening again. All deliveries of wood to the site have currently been suspended.”