Malaysians have been advised to stay indoors after smoke haze cloaked the capital, Kuala Lumpur, and surrounding areas.

Hospitals are on the alert for health problems.

On Wednesday, the air quality in the Malaysian capital and surrounding areas was declared "unhealthy".

The haze moved over Kuala Lumpur and the surrounding Klang Valley on Tuesday, covering the Petronas Towers and permeating buildings with the smell of smoke.

The Environment Department says the problem is being caused by hundreds of fires in the Indonesian provinces of Kalimantan, Riau and northern Sumatra, as well as Malaysia's eastern state of Sarawak.

Peat fires, which started on Monday in Cyberjaya, south of Kuala Lumpur, have also contributed to the smoky conditions in and around the capital.

However, environmental authorities say the number of fires in Sumatra has dropped and the smoke is now easing.

Haze caused by fires in Indonesia and Malaysia is a common occurrence during hot, dry seasons.