At least two persons were injured on Wednesday morning near Sonipat town, 50 km from Delhi, in a pile up of cars on a busy National Highway (NH-1), police said.
Dense fog was reported from several areas of the NH-1 between Ambala and Kundli border of Haryana and Delhi.
A few trains were running behind schedule due to the fog.
In Punjab, fog was reported from some parts.
The minimum temperature at most places in Haryana and Punjab hovered around 7-8 degrees Celsius.
Met officials here said that the foggy weather will prevail over the next few days.