A huge sandstorm and record winds killed at least four people Monday in Tehran, plunging Iran's capital into darkness during rush hour and forcing thousands to run for cover.

The freak weather struck at 5:10 pm (1240 GMT), knocking down trees and sweeping other debris across streets and into the windscreens of cars as people headed home from work.

State media reported 110 kilometre (70-mile) per hour winds at the peak of the disruption.

Power supplies were knocked out in at least 50,000 homes, an electricity official said, and the weather smashed windows and caused telecommunication towers to topple and masonry to fall off buildings.

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

Amin Saberinia, 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 of those injured in the storm were in critical condition.

"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 told an AFP reporter 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.

Almost 7,000 emergency workers were deployed within the hour, city officials said, and Ahad Vazifeh, in charge of government weather forecasts, cautioned of more bad weather lasting into Wednesday.

After a 15-minute blackout caused by the initial force of the sandstorm hit, rains arrived with winds remaining strong.

Pictures posted on social media showed a gigantic sand cloud filling the city's skyline, before it turned dark and outside temperatures plunged from 33 degrees Celsius (91 Fahrenheit) to 18 degrees.

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 safety, staying on in office buildings before venturing out.

With the storm arriving as the work day ended, road monitoring services showed large areas of Tehran gridlocked shortly after the worst of the weather.

Although the streets seemed largely back to normal by 1500 GMT, the reports of more bad weather were being closely monitored, state television said.

Crews from Tehran's fire department also joined the clean up effort.