NEW DELHI: School holidays have been extended till January 15 in Delhi and UP, where extreme cold continues. 267 trains were cancelled in North India yesterday. 150 flight services were delayed in Delhi, while three were diverted to Jaipur. The minimum temperature in Delhi is 3 degrees Celsius. Delhi's air quality deteriorated to the 'severe' category. A ban has been imposed on BS III petrol and BS IV diesel vehicles from today.