BEIJING, Dec. 12 -- Smog-choked Chinese capital Beijing announced an ambitious plan Thursday to phase out all oil-burning buses in downtown area by 2017.

With an expected investment of 10 billion yuan (1.64 billion U.S. dollars), the city plans to buy 13,825 new buses in the next few years, all of them driven by either electricity or natural gas, the city's transportation and environment protection authorities said.

By 2017, 66 percent of the total 21,000 buses in the city will be electronic or clean energy buses. About 150,000 tonnes of fuel oil will be saved every year, and carbon emissions cut by 50 percent.

The rest of the buses will be low-emission diesel vehicles.

The city plans to purchase a new type of trolley bus that will be powered either through overhead cables or onboard lithium ion batteries, said Cao Yan, operational manager of the Beijing Public Transportation Group. The trolley bus will be able to run for 8 to 10 hours offline.