Air quality in Malaysia and Singapore has steadily deteriorated over the past two weeks due to the smog from nearby regions of Indonesia, which yesterday declared a state of emergency in a particularly hard-hit province.
Malaysia's education ministry ordered schools closed in Kuala Lumpur, three adjacent states and the nearby administrative capital of Putrajaya, where air pollution indices were in the upper range of "unhealthy" and nearing "very unhealthy".
More than half of the country's 52 monitoring stations registered "unhealthy" air today.
Indonesia has declared a state of emergency in Sumatra's Riau province.
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Tens of thousands of people in smoke-choked regions of Sumatra and Borneo have fallen ill, while air travel there - as well as in parts of Malaysia - has been hit by sporadic flight delays or cancellations due to poor visibility.
Malaysian authorities in several areas have distributed free face masks, while the marine and aviation sectors have been advised to go on high alert due to the worsening visibility.
Indonesia has come under pressure to control the annual smog outbreaks but joint regional efforts have failed to find a lasting solution.