JAKARTA, March 11 (Bernama) -- Up to 20,000 hectares of forest in Sumatra's Riau province are on fire and there is fear the smoke may soon result in a haze in Malaysia, as had happened in the past.

Already, the Riau capital of Pekan Baru has been enveloped by thick smoke which, according to several residents, had been present over the last two weeks.

Local newspapers have reported the detection of more than 100 hotspots (signs of fires) on satellite images of an area along the border of Riau with northern Sumatra.

The forest fires are reportedly spreading fast, with the affected area doubling in size in a matter of only three weeks.

A spokesman of the Riau Department of Environment was quoted by the "Detiknews" news website as saying that the forest fires covering more than 20,000 hectares had enveloped several districts in the province with smoke though visibility was still at one kilometre.

"The most widespread fire has occurred in Dumai on the Strait of Melaka and our team on the field has found many hotspots in the forest that had been cleared and long abandoned," he said.

The spokesman said the cause of the forest fires, which also covered the districts of Bengkalis, Indragiri Hulu and Rokan Hilir, was being investigated.

Meanwhile, a spokesman of the Riau meteorological and geophysics authority said the province was experiencing a drought and the smoke from the forest fires could spread easily.

However, the prevailing Southwest Monsoon had yet to carry the thick smoke across the Strait of Melaka, he said.

Over the last few years, Malaysia had felt the effect of the forest fires in Riau when the monsoon carried the thick smoke across the strait and enveloped a part of Peninsular Malaysia with haze, forcing Malaysia to send its firemen to Riau to help put out the fires.