Delhi Police said six people died and 13 were injured in various areas of the city in accidents like felling of trees, collapse of walls and electrocution following the storm which was accompanied by winds at a speed of over 90 kmph.
The storm struck Delhi at 4:58 PM immediately throwing normal life out of gear.
Thousands of people were stranded outside Metro stations and on roads as traffic almost came to a halt due the storm which darkened the sky.
Met department termed the storm as "cumulonimbus" and attributed it to western disturbance over Pakistan. NCR areas of east Delhi, Noida and Ghaziabad were most affected by the storm.
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Met office said similar weather conditions are likely to persist for over the next two days. At least 12 flights were diverted due to the storm, an IGI official said.
Areas in South, East and North Delhi faced long power cuts ranging from one to four hours. Supply of power could not be restored till late in the evening in several areas in North and North West Delhi.
"The cumulonimbus brings tall thunderstorms and dusty winds with a speed of over 92 kmph and are caused because of western disturbance, which is currently over Pakistan.
"The meeting of cold air and hot air on the Indo-Gangetic plains causes low pressure area and also lot of instability. This results in severe thunderstorm," IMD Director General L S Rathore said.
The storm affected northeast Haryana and the NCR. But parts of east Delhi, Noida and Ghaziabad were affected the most, he said.