According to the India Meteorological Department, the visibility stood at 50 metres at 8.30 a.m., while the minimum temperature was recorded at seven degrees Celsius, two notches below the season's average.
The humidity at 8.30 a.m. was 100 per cent. A moderate fog was forecast for the day ahead.
At least 18 trains were cancelled, 35 delayed and two were rescheduled due to fog in several parts of northern India.
The maximum temperature was likely to hover around 18 degrees Celsius. Moderate to dense fog was likely around evening, a Met official said.
Maximum temperature on Thursday was recorded at 18.4 degrees Celsius, four notches below the season's average while the minimum temperature settled at 8.8 degrees Celsius, two notches below the season's average.