A metro train approches a station during a thick smog in Gurgaon, a suburb of New Delhi on December 29, 2017. Pic/AFP

It was a foggy morning here on Sunday with the minimum temperature recorded at 6.4 degrees Celsius, a notch below the season's average, the weather office said. At least 15 trains were cancelled, 57 delayed and 18 rescheduled due to fog in several parts of northern India. The humidity at 8.30 a.m. was 97 per cent and visibility stood at 400 metres. "The sky would remain clear in the day ahead," an official of the India Meteorological Department said.