With offices in the urban sprawl of 10 million people effectively shut down through the weekend until Saturday, police were also out in force to prevent motorists from entering a large part of the city without a permit.

Officials hope that will help clear a hideous blanket of brown-yellow haze -- denser than usual this week due to a total lack of wind.

"The air situation is really acute, but it is expected to get better after the shutdown," Tehran city council member Amir-Reza Vaezi-Ashtiani told AFP.

"We've spelled out our complaints in the city council, and the officials concerned have to deal with this dangerious issue. No institution has done enough and each blames another. That's why Tehran is suffering."

The government has proposed various steps to resolve the worsening public health menace, such as phasing out the old cars, mandatory emissions checks and restricting vehicle use on certain days of the week. So far, no measure has been effectively enforced.

But with the city choking on its own fumes, Tehran's traffic police chief General Sajedinia said attitudes were changing.

"The citizens who violate today's expanded ban on entering restricted traffic areas will be fined," he told state television.

"If the pollution continues at this level, the rule of driving on certain days of the week based on even and odd car license plate numbers will be put in force," the general warned.

Many of the two million plus vehicles in the city are more than 20 years old and guzzle cheap subsidised petrol -- which costs a paltry nine US cents a litre, or 34 cents a gallon -- at an alarming rate.

Private car ownership has also exploded and the public transport system does not provide adequate coverage to many parts of Tehran.

Rampant construction work has also contributed to the smog, with building sites churning out dust into the atmosphere.

Pollution alerts are becoming increasingly common in the city, with air quality deemed unhealthy for at least 100 days of the year. Complaints of asthma, allergies and respiratory ailments are also on the rise.

The holiday order is unprecedented: previous pollution alerts have only prompted local authorities to close schools and tell the sick and elderly to stay indoors.

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