Dense fog over northern India led to total blackout in many parts of Punjab, Haryana and Jammu and Kashmir on Saturday morning due to disruption in transmission lines.

The northern grid tripped at around 3.02 am following a technical snag in transmission lines that reduced power to zero at many sub stations, Power Grid CMD S K Chaturvedi said.

"There were disruptions in 220 KV system transmission line because of the fog over Punjab due to which power was zero at some sub stations. However, NCR lines were saved because we had already taken some precautionary steps like cleaning of transmission lines in advance," Chaturvedi said.

Power supply was disrupted in Ropar, Bhatinda, Yamuna Nagar and Panipat power stations, which are connected to the northern grid.

However, by 7:30 am electricity was partially restored in some parts of Punjab and Srinagar after supply from Jalandhar, Nathpa and Uri sub stations were diverted to these states.

Power is yet to be restored in smaller towns like Moga.

"As the state government of Punjab does not have such provisions (clean up transmission lines in advance), there was a loss of 5,500 MW of electricity at Ropar, Bhatinda, Yamuna Nagar and Panipat power station which are connected to the northern grid," he said.

He said, the Delhi-NCR line is totally safe and work is going on to restore supply in the rest of the region.