KUALA LUMPUR, Oct 9 (Reuters) - Malaysia on Monday warned ships sailing through Asia's busiest waterway to guard against accidents as a choking smog smothering the region cut visibility.


Visibility along the narrow Malacca Strait, which links Asia to the Middle East and Europe, has been sharply reduced to less than one mile (1.6 km) from a usual 12 miles (19 km), as smoke from raging Indonesian forest fires showed no signs of abating.

The Strait, traversed by more than 50,000 ships a year, carries 40 percent of world trade, including 80 percent of the energy supplies of China and Japan.

"We have alerted ships using the strait to take extra care due to the poor visibility," said an official of the Malaysian marine department. "This is dangerous for small boats, but so far there has been no incident."

The forest fires, concentrated on the islands of Borneo and Sumatra, are a regular occurrence in the dry season but appear to have worsened this year with fires on highly flammable peatland and amid a hot spell ahead of the start of rains due this month.

Thick haze blanketed much of peninsular Malaysia on Monday, with the capital's iconic Petronas Twin Towers barely visible from a distance of 3 km (2 miles). The Subang airport just outside Kuala Lumpur was closed to small planes as visibility fell to just 1.5 km (1 mile), an airport official said.

But the main Kuala Lumpur international airport was operating normally. "So far, there are no delays in landing or taking offs," another airport official said.

Air pollution in Malaysia has yet to reach the levels of 1997, when mainly Indonesian fires blotted out skies across Southeast Asia.

The 1997-98 smog cost local economies billions of dollars and left many people ill. The fires over that period destroyed five million hectares (12 million acres).

HEALTH CONCERNS

In Sumatra, thick haze from forest fires forced the main airport in Riau province on the island to close on Sunday, the Koran Tempo newspaper reported. Passenger ferries in the province also were delayed when haze shrouded the main seaport.

Lily Sadiah Aryanto, the head of the health office in Pontianak, the capital of West Kalimantan in Borneo, said the number of acute respiratory infections have risen this year.

"Haze this year is denser. People are coughing, have colds and sore throats. In some cases the skin turns red, while eyes are painful and water," she told Reuters.

The haze situation in Singapore improved on Monday, after the Indonesian fires sent air pollution in the city-state over the weekend to its worst levels in nearly a decade.

The air pollution index fell back to a healthy range to stand at 45 based on a three-hour average reading on late Monday morning from a high of 109 on Sunday, a three-hour average reading by the National Environment Agency showed.

An agency spokeswoman said people with heart and respiratory ailments should avoid outdoor activities.

The thick haze blowing across from Sumatra had prompted authorities to post a health advisory on Saturday, warning people to scale back vigorous outdoor activity. (Additional reporting by Sebastian Tong in Singapore and Diyan Jari in Jakarta)