With the air quality officially classified as "unhealthy", the National Security Council said it was monitoring the situation and prepared to intervene if it moved to the "hazardous" level of above 300 on the air quality index.

When "it comes over 301, the national security division will take charge of handling the disaster," an official told AFP.

This could include restricting working hours and closing schools, he said.

The crisis is being blamed on peat fires outside Kuala Lumpur, as well as hundreds of blazes in Indonesia's Riau and North Sumatra provinces, and Borneo island.

As visibility in the busy Malacca Strait plummeted to less than one kilometre (0.6 miles), The Star daily said a container ship had run aground in the murky conditions and that operations at two major ports were interrupted for hours.

"We have issued a warning for shipping activities in the Strait of Malacca. The warning is that the visibility is hazardous to ships without navigational equipment," said Meteorological Department official Wong Teck Kiong.

Newspaper reports said that visibility fell to just 100 metres (yards) in the worst-affected areas Tuesday, forcing motorists to turn on their headlights.

Wong said that only the October monsoon season would shift the haze, as the southwesterly winds bringing smoke from Sumatra would not change direction until then.

"The next few days we expect the same situation, which is a stable atmosphere and no rain," he said, although there could be some relief at the end of the week.

Newspapers said reports of respiratory tract infections, conjunctivitis and sore threats were flooding in over recent days.

The education ministry has given permission for schools to close if they believed the haze was bad enough.

"It is up to the teachers to decide what is best for the students," ministry official Hishammuddin Hussein said according to the New Straits Times.

Under the air quality index, less than 50 is good, 51-100 is moderate, 101-200 is unhealthy, 200-300 is very unhealthy and more than 300 is hazardous.

Malaysia has banned the release of exact figures for fear of damaging its tourism industry, but rights groups on Wednesday demanded that they be more accountable.

"Not wanting to scare tourists is not a good enough reason to not release the index," Meena Raman from Friends of the Earth Malaysia told The Star.

"There is no information on how the authorities are cooperating with the Indonesian government to stop the problem from becoming an annual event," she said.

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