Acrid smoke from a 2,000 tonne rubbish fire in Vale of Glamorgan has reached as far as Bridgend, Barry and Cowbridge, the fire service has said.
The blaze at Llandow Industrial Estate started on Thursday and is continuing to burn under supervision.
Residents are being advised to keep windows closed.
South Wales Fire and Rescue Service said the risk to health is thought to be low but the smoke could cause nose and eye irritation, and coughing.
On Friday night, three crews were still on site and the fire is expected to continue through the weekend.
The service tweeted "slow progress being made due to poor water supply".
Vale of Glamorgan council said a minor road leading to the site had been closed but others had reopened.
Nearby schools were advised to open as usual and there is no impact on the water supply.
Public Health Wales (PHW) experts said they were monitoring the situation.
Andrew Kibble said: "If you live in an area affected by smoke, stay inside and close all doors and windows. This will greatly reduce your exposure to the smoke.
"If you have to go outside, try to keep away from the areas affected by visible smoke or ash."
He added motorists should keep their windows shut, turn off air-conditioning and keep air vents closed.
He said PHW was not aware of any reports of people experiencing ill-effects from the fire as yet.
The council's emergency planning team is also working to limit disruption.