Private vehicles will only be allowed on Delhi's roads on alternate days from January, authorities said Friday, as the world's most polluted capital tries to clean up its fetid air.

The Delhi government will also improve public transport in the city, shut down a coal-fired power station and start vacuuming the roads to reduce dust, said chief secretary KK Sharma.

"Every year, the pollution level goes up in winter. Now for the last several weeks and before that also... we have been working to find a solution (to) this problem," he told reporters after an emergency meeting of the state government to discuss the crisis.

"Particularly in winter, when the pollution is high, we will implement for some time odd and even number vehicles operation."

He said the government would aim to start the scheme on January 1 and that the restrictions would initially be temporary.

"Let us see how it rolls out," he added.

There are already more than 8.5 million vehicles on Delhi's roads and 1,400 new cars being added every day, contributing to some of the worst pollution in the world.

Several Chinese cities have slapped limits on car numbers because of congestion and pollution, but it is the first time the Indian capital has implemented such a measure.

The decision to restrict private cars came two days after India's environmental court ordered the Delhi government to come up with a strategy to tackle the smog that has settled over the city in recent weeks.

- World's worst air -

Successive Delhi governments have faced flak for failing to clean up the filthy air, ranked as the worst in the world in a World Health Organization survey of more than 1,600 cities.

The issue has been in the spotlight this week as negotiators from 195 nations haggle in Paris over a planned universal accord to slash the greenhouse-gas emissions that trap the Sun's heat.

India has said poor countries cannot be expected to make the shift away from cheap and abundant fossil fuels at the expense of struggling populations, many of whom do not even have access to electricity.

Environmental campaigners welcomed the Delhi government's plan, but said it would be tough to implement.

"I think it (government) has taken the serious measures that are needed to deal with Delhi's air, we have an emergency-type situation and I'm glad the government is stepping in," Sunita Narain, head of the Delhi-based Centre for Science and Environment, said on the NDTV news channel.

"It's very important for us to recognise the fact that these may be tough measures, they will be difficult to implement, but that is what governments are for and it has responded to a public health emergency. That is very good."

Delhi's air routinely worsens in the winter as residents start lighting fires to stay warm and as cooler air and clouds trap pollutants.

But unlike Beijing, which also suffers from hazardous haze levels, the city does not issue public health warnings.

Courts have been pushing authorities to act, including ordering a toll tax on the thousands of diesel-guzzling trucks entering the city every night.

Sharma said city authorities would begin vacuuming the roads in April, citing dust as a major contributor to poor air quality.