A choking smog that has enveloped New Delhi for more than a week has been partially caused by a rapid increase in vehicles on the streets of India's capital, environmentalists said Wednesday.

With temperatures falling after the hot summer, a thick haze of dust and pollution has been trapped in the city with residents complaining of toxic air quality.

"Everyone is buying cars and motorbikes because the government is taking a long time to scale up its public transport system," Anurag Trivedi, a researcher at the Centre for Environment Studies, told AFP.

"The pollution is choking all of us," he said, adding that according to official figures more than 1,000 new vehicles hit the roads of Delhi each week.

The Supreme Court on Tuesday raised an alarm over the problem, and said it intended to take action for the sake of the 17 million people who live in the rapidly-expanding city.

"We are concerned with the level of smog in the city. Every day we are hearing about the rising level of pollution," Chief Justice Altamas Kabir said. "We will deal with the matter."

Officials at the meteorological department said the thick cloud of smog was dust and pollution gathering in the city due to the seasonal lack of wind.

"The real trouble is that smog during winter cannot escape to the upper atmosphere as it can during other seasons," said B.P. Yadav, a weather officer.