Helicopters have been used to water bomb the fire

Helicopters were used to waterbomb the blaze at Loudon Hill, which at one stage covered a 13 square kilometres (8 sq miles) area of forest and moorland.

About 100 firefighters were called to the fire near the village of Darvel.

It is one of more than 100 similar fires across the country, which are thought to be caused by the hot weather.

'Endangering homes'

A lack of air cover hampered firefighters efforts to contain two major hill fires in the Highlands.

Crews in Lochaber were fighting a blaze stretching along a 10-mile front between Salen and Acharacle.

At Laggan near Newtonmore, efforts were made to prevent a major fire re-igniting a forest plantation badly damaged on Thursday night.

Neighbouring firecrews from Dumfries and Galloway, Lothian and Borders, as well as a third helicopter from Devon, were drafted in to assist with the Ayrshire blaze.

Strathclyde Fire Brigade's assistant firemaster, Phil Robinson, said the fire was one of the biggest he has dealt with.

He said: "It is not endangering homes at the moment, but given the wind direction and speed of the fire, there is the potential for that to happen.

"We are paying close attention to that and will make sure that if any homes are likely to be involved, they will be evacuated long before there is any danger to life."

Mr Robinson added: "It is a very difficult type of fire to fight because of the weather conditions, the dryness and the vegetation.

Being one of the largest brigades in Europe we are able to cope with this but it really is stretching our resources. Phil Robinson Strathclyde Fire Brigade

"The weather is so hot and everything is so dry it could have been started by a cigarette end or anything."

A large blanket of smoke hovered over the nearby village of Darvel, in stark contrast to the surrounding clear blue skies.

The public are being urged to take care when discarding glass litter, matches and cigarettes.

Mr Robinson said: "I would like to stress at this present time, for people to be careful and protect the countryside."