BEIJING -- Beijing phased out more than 4,450 coal-fired stoves in 2017, reducing the capital city's coal consumption by nearly 3 million tonnes, local authorities said Friday.

The move also reduced emissions of 5,500 tonnes of smoke and 6,600 tonnes of sulfur dioxide, the Beijing Municipal Environmental Protection Bureau said.

As part of a campaign launched in 2013, Beijing has phased out about 99.8 percent of coal-fired stoves in the city. Natural gas and other forms of clean energy are used to replace coal.

Environmental monitoring results show that Beijing's average sulfur dioxide density, a major air pollutant, was 8 micrograms per cubic meter towards the end of October 2017, compared with the annual average density of 28 micrograms in 2013.

Small stoves in Beijing's suburban and rural areas, not covered by the central heating system, had been blamed for worsening the city's smog during the winter.

Beijing completed 338 projects to switch coal-fired heating to heating fuelled by natural gas in rural areas this year, involving 8.5 billion yuan ($1.3 billion) of investment.