Residents living near Saddleworth Moor have reported problems including bleeding noses, eye irritation and chest problems as the moorland fire continues, a GP has said.
Dr Richard Bircher, of Lockside Medical Centre in Stalybridge, said about half the emergency appointments booked on Thursday were from patients reporting problems as a result of the smoke.
He said the smoke was also exacerbating problems for people with asthma.
As firefighters said the blaze could potentially last for days, if not weeks, Dr Bircher said people should continue to take the advice.
But he said the community had come together to offer places to stay for those living near the fire and to collect donations of food and water for firefighters.
Public Health England has issued advice for residents, which warns them to close doors and windows if there is visible smoke and draw curtains to limit sunlight heating up homes.
They are also advised to keep hydrated, wear light clothing and use fans to recirculate air in the house.
Anyone with a heart or lung disease, such as asthma, is warned to ensure they have access to medication and seek medical advice by calling NHS111 if symptoms worsen.
Dr William Welfare, consultant in health protection for Public Health England said:
Experts have said the fire is generating tiny particles of pollution known as "particulate matter", which can cause sore throats, eye irritation and breathing difficulties.