Chongqing in southwest China will open its first subway line by 2011, local authorities said on Thursday.

A 36.08 km line with 22 stops will be built in the downtown area of the mountainous municipality at a cost of 12.5 billion yuan (1.8 billion U.S. dollars), according to its urban planning bureau.

Construction on the first phase of the line, about 16.5 km in length, began last year. It was expected to be completed and operational by 2011.

Workers will start building the remaining part of the line next year, but it was not clear when it will finish.

Chongqing is one of four municipalities in China directly under the jurisdiction of the central government. The other three are Beijing, Shanghai and Tianjin. Chongqing is the largest with an area of more than 82,000 sq km.

The city currently has a 19.15 km of light rail in operation. Another light rail is under construction and is expected to be open by 2010.

As a well-known "mountain city" in China, Chongqing has lots of narrow and zigzagging roads with slopes, slowing traffic flow. Citizens have been longing for a subway system for years.