NEW DELHI - Heavy fog in Delhi on Monday delayed flights, and a cold wave forced the authorities to defer school reopenings by a week, as visibility fell and cars drove with their hazard lights on.

The Indira Gandhi International Airport in the Indian capital asked fliers to contact their airlines for updates on flights.

“Due to dense fog, flight operations at Delhi Airport may get affected,” it said on Twitter.

Meanwhile, data from private flight trackers showed several flights had been delayed.

The India Meteorological Department (IMD) forecast “dense to very dense fog conditions” over many parts of Delhi and northern and eastern states, such as Punjab, Haryana, Uttar Pradesh and Bihar, until Tuesday. It warned that air, road and train traffic could be affected in the two days, and people could suffer from lung-related health problems. It also said power lines could trip in areas with dense fog.

Delhi, a city of 20 million people, has already extended winter holidays for many schools by a week. Many private schools were to reopen on Monday.

The city recorded a minimum temperature of 5 deg C on Monday. The lowest for Sunday was 3.8 deg C, which the IMD said was three degrees below normal for this time of year.

A cold wave is declared in the plains of India when the minimum temperature dips to 4 deg C or falls 4.5 degrees below normal to 10 deg C or below. REUTERS