Haze caused by Indonesia's wildfires has reached a far wider area in the southern Philippine island of Mindanao than earlier reported.

Thin layers of greyish cloud consistent with haze were observed yesterday in parts of Sarangani, South Cotabato and Sultan Kudarat provinces in the southern half of Mindanao, news network ABS- CBN reported.

Haze was earlier reported to have blanketed the cities of Davao and General Santos in southern Mindanao, and a third city, Cagayan de Oro, farther north of the island.

Weather officials said monsoon winds blowing north-east could be causing smoke and dust from nearly a thousand forest fires in Indonesia's Kalimantan region 1,000km away to drift towards Mindanao.

Wind patterns created by Typhoon Koppu, which pummelled the northern Philippines for four days from last Saturday, might have also created a pathway that carried the haze from Kaliman- tan to Mindanao.

Early this month, metropolitan Cebu in central Philippines was enveloped in a bluish-grey and unusually thick layer of haze for more than a week.

Meteorologists at the time said the haze had actually spread across Mindanao as well, but it was thickest and most visible in Cebu because of a pocket of air created by a tropical storm and local pollution over the city, home to over four million.

Cebu officials issued health advisories while the civil aviation authorities grounded small planes incapable of landing without pilot assistance.

The haze across Mindanao has not been as thick as in Cebu, and local officials said it does not pose any health risk. "There is no reason to be alarmed," said weather forecaster Gerry Pedrico.

Dr Herry Purnomo, a scientist at Indonesia's Centre for International Forestry Research, said 30 million people in Indonesia, Singapore, the Philippines, Malaysia and Thailand have been affected by the haze so far this year.

"It is as bad as what happened in 1997, 1998 and 2006," he said.