Schools in New Delhi have been ordered closed as a suffocating, toxic haze engulfs the capital.

City authorities imposed the toughest anti-smog controls on Monday as pollution levels worsened to the emergency "severe plus" category.

Children, the elderly and vulnerable people have been urged to stay home. Students are taking classes online, apart from those who have important exams coming up.

Few people venturing outside wear masks. Even the high-protection variety don't offer a perfect defense against the soot-laden air, as a woman wearing one such mask who was walking near the India Gate war memorial pointed out. She said she didn't have a cold, but her nose was blocked, her eyes were burning and smog had got into her hair. "It's the worst," she said.

Air quality in northern Indian cities plummets at this time of year. It gets worst around Diwali, the biggest Hindu festival, celebrated with fireworks and firecrackers. Cool temperatures, farmers burning stubble and vehicle emissions are also major contributors to the miasma.