NEW DELHI: Overnight rain in New Delhi and its suburbs brought some relief to the Indian capital on Friday morning, where authorities were mulling seeding clouds to improve the toxic air gripping the city.

The city, which was the most polluted in the world till Thursday, saw its air quality index (AQI) improve to 127 early on Friday - a welcome change from the "hazardous" 400-500 level seen during the past week, according to Swiss group IQAir.

India's weather department has forecast intermittent rain over the city and adjoining areas till early noon on Friday. Light showers are also expected in neighbouring states like Punjab, Haryana, and Rajasthan.

On Friday morning, New Delhi was the 10th most polluted city in the world while Kolkata in India's east topped the global chart with an AQI of 303.

Meanwhile, air in the financial capital of Mumbai has markedly improved due to showers in nearby coastal areas.

This year, attention on the worsening air quality has cast a shadow over the cricket World Cup hosted by India.

Scientists and authorities were planning to seed clouds in New Delhi around Nov. 20 to trigger heavy rain, the first such attempt to clean the air.

A thick layer of smog envelops the city every year ahead of winter as heavy, cold air traps dust, vehicle emissions and smoke from burning crop stubble in Punjab and Haryana.

Friday's rain comes two days before the Diwali festival, when many people defy a ban on firecrackers, causing a spike in air pollution.

The local government of the city of 20 million people, spread over roughly 1,500 square kilometres (579 square miles), has already shut all schools, stopped construction activities, and said it will impose restrictions on vehicle use to control pollution.