Marzieh Vahid Dastjerdi – the only female minister in President Mahmoud Ahmadinejad’s government – issued the drastic advice as soaring pollution levels prompted a rise in hospital admissions and the emergency closure of schools, universities and government agencies.

“If Tehran’s inhabitants are able to leave the city, it would be good for them to do so,” she said, according to the Arman newspaper.

Her comments came after Tehran, one of the world’s most polluted and traffic-clogged cities, was enveloped by a choking poisonous haze which experts say was severe even by its standards.

Hospitals recorded a 15 per cent increase in admissions as doctors were called on to treat patients suffering from respiratory ailments, headaches and nausea.

Amid a flurry of official warnings, even Mr Ahamdinejad was forced to cancel the government’s weekly cabinet meeting.

It is not the first time the Iranian city’s authorities have been forced into such measures.

In 2006, officials estimated that 120 people had died from pollution-related illnesses every day in the months of October and November alone.Tehran’s official responsible for clean air at the time described life in the city as “mass suicide”.

Air quality can decline significantly during the winter as a combination of cold, still air and the surrounding mountains produces a film of trapped smog that reduces visibility to a few hundred metres, driving many residents to wear face masks. Large numbers of motorbikes and elderly Peykan cars – modelled on the British Hillman Hunter and often without air-filters – are thought to be a contributing factor.

Despite Mrs Vahid Dastjerdi’s advice, it remains to be seen how many residents resort to the action once taken by Tehran’s black crow population, which according to environmentalists, fled in a mass exodus in 2008 during a pollution outbreak.