Long lines of vehicles have been snaking through Rohtang Pass as residents flee Delhi, widely regarded as the world’s most polluted capita, in search of cleaner air, overwhelming normally quiet mountain routes.

Footage showing cars inching along the pass in Himachal Pradesh in late December went viral on social media, the Times of India reported.

There has been no snowfall and the peak holiday season has not begun but large numbers of people are flocking to the mountains as air quality index (AQI) levels in Delhi repeatedly reach hazardous levels.

Vamika Grover, 32 and a survivor of Hodgkin’s lymphoma, is among those leaving, Foreign Policy magazine said.

"I’ve been feeling a sense of breathlessness these past few years, and I would feel my lungs would have to do a lot of heavy lifting... It’s polluted throughout the year now, and it’s creating health issues for everyone," she said.

Since October, AQI levels in Delhi have regularly exceeded 300, three times above the safe threshold, with readings in some locations rising above 1,000.

In late October, an Indian pulmonologist advised people with chronic lung or heart conditions to leave Delhi for six to eight weeks.

The climate exodus is creating new pressures in mountain areas. Previously quiet towns such as Mussoorie and Landour are facing traffic congestion, overcrowded parking and a surge in construction to serve those escaping air pollution, India Today said.

Professor Kapil Joshi of IIT Roorkee warned of environmental impacts in these areas.

"Heaps and heaps of disposables along with plastics and bottles may be seen all along the roadside.

"A large portion of that either remains on the road or ends up at some water spring or river," he said.

Climate data show that mountain resorts are also warming. Dr. Anil Joshi, an environmental conservation expert, said AQI levels in Dehradun, at the foothills of the Himalayas, now frequently range between 150 and 300.

Demand for second homes in cooler regions has surged, causing sudden population increases and putting pressure on water resources and public services.

As authorities consider measures such as air purification towers and mist spraying, which critics say have limited impact, people like Vamika Grover have chosen to leave permanently.

"If I were to choose my life and health, I wouldn’t pick Delhi," she said. (VN Express)