Air pollution levels have shot up across the Indian capital to severe-to-critical levels, a day after fireworks during the Hindu holiday of Diwali, leading to a string of health warnings.

Such pollution happens every year, as offices and businesses shut down for India's biggest gift-giving holiday and many gather outdoors to set off powerful rockets all throughout the night.

A government health advisory Thursday warned people to avoid all outdoor physical activity, citing a serious risk of respiratory effects from a prolonged exposure to smoke-filled air.