Tesla Inc plans to start manufacturing electric vehicle (EV) chargers in China in 2021, according to a document submitted to the Shanghai authorities by the US firm which is seeking to expand sales in the world's biggest car market.

Tesla, which now sells its Model 3 electric cars in China and plans to deliver its Model Y sport utility vehicles in 2021, plans to invest 42 million yuan ($6.4 million) in a new factory to make the chargers, also known as charging piles, near its car plant in Shanghai, the document seen by Reuters said.

China, which offers hefty subsidies for electric vehicles as it seeks to cut down on pollution from petrol or diesel cars, has been expanding its nationwide network of charging points, one of the biggest challenges to encouraging adoption of EVs.

The factory, which Tesla expects to complete in February, will have capacity to make 10,000 chargers a year, according to the document submitted by Tesla.

It now imports the chargers, usually installed in charging stations or car parks, from the US.

Tesla, which sold over 13,000 vehicles in China last month, did not immediately respond to a request for comment.

The Shanghai car factory, central to Tesla's global growth strategy, aims to produce 150,000 Model 3 sedans this year and has started exporting some vehicles to Europe.

Executives at Tesla said this year that the firm would expand its charging network to provide better service.