NEW DELHI — Extreme cold and dense fog have caused travel chaos in India's capital Delhi and other parts of northern India.

More than 100 flights and 25 trains in the city have been delayed due to poor visibility.

The city witnessed one of the foggiest days of the season so far, with visibility dropping to below 50 metres on Wednesday.

A thick blanket of mist in the morning brought traffic to a crawl and also led to accidents in some parts.

Accidents have been reported from other parts of north India as well.

In the neighbouring Uttar Pradesh, multiple vehicles collided on a prominent expressway on Wednesday morning as a dense fog swept through the state.

Photos and videos from the site showed crumpled parts of a car lying on a misty road. Several people have been reportedly injured in the crash but there are no casualties.

Dense fog is common in the region at this time of the year as various parts of northern and central Indian experience cold waves.

Cold weather is also continuing in most parts of the northern states of Punjab, Haryana, Uttar Pradesh, Madhya Pradesh, Rajasthan, and in Indian-administered Kashmir.

India's weather office has issued an alert, saying the foggy conditions would continue for the next five days.

In its advisory, the department asked people to be cautious while driving and urged them to use fog lights for enhanced visibility on the roads.

It has also asked people avoid going out unless there is an emergency and to cover their faces adequately when outdoors.

The extreme cold is particularly hard for India's homeless population, who often sleep beside the road and at railway stations. — BBC