Sandstorm kills at least 4 in Iran capital

A massive sandstorm and record winds have killed at least four people in Tehran, plunging the Iranian capital into darkness, knocking out power supplies, damaging buildings and causing massive disruption.

The freak weather struck at 5.10pm (2240 AEST), sending residents dashing for cover as debris swept across streets and snapped trees on Monday.

State media reported 110 kilometre per hour winds.

Forecasters on state television initially warned Tehranis to stay indoors, shortly before the ISNA news agency said the fatalities were caused by falling trees.

Amin Sabernia, Iran's chief emergency official, announced the deaths and said at least 27 people were injured, 10 of them in a road accident when the gloom suddenly descended.

State television later reported that two people injured in the storm were in critical condition.

Almost 7000 emergency workers were deployed within the hour, city officials said, and Ahad Vazifeh, in charge of government weather forecasts, cautioned of bad weather until Wednesday.

"This is like an apocalyptic Hollywood movie. I'm scared," a woman running into a shop in the capital's central business district to escape the gales said seconds after the storm hit.

A man inside the same building said: "I've never seen anything like this. I was afraid it was an omen of things to come."

Residents of earthquake-prone Iran usually make such comments when they fear a strong tremor is imminent.

After a 15-minute period of gloom caused by the sandstorm began to lift, rains arrived with winds remaining strong.

Pictures posted on social media showed a giant sand cloud approaching the city, before it turned dark and the outside temperature plunged from 33C to 18C.

An electricity official quoted by the ISNA news agency said power had been lost in at least 50,000 homes.

Flights out of Tehran were delayed, Fars news agency said, quoting airport officials.

Internet and telephone services were heavily affected, with lines going down before returning intermittently.

About 90 minutes after the initial storm, the winds appeared to ease and more cars were seen on the streets, although many people opted for caution, staying on in office buildings.

With the storm arriving as people were headed home in rush-hour traffic, road monitoring services showed large areas of Tehran gridlocked shortly after the worst of the weather.