New Delhi:  Thick winter fog disrupted travel across northern India on Sunday, with international flights out of New Delhi airport severely delayed and train schedules thrown into chaos.

About 15 domestic flights were cancelled and 12 international flights were delayed due to poor visibility at the airport. Seventy-five flights were affected.

"Dense fog enveloped the city since the early hours today and the visibility at the Indira Gandhi International airport dropped to near zero, heavily disrupting (flights)," the Press Trust of India news agency reported.

Train journeys in Punjab and Haryana state were also badly affected, with thousands of passengers stranded or facing delays.