Beijing has begun testing a new subway line as part of a multi-billion dollar upgrade to the capital's infrastructure ahead of the Olympic Games in August.

The first phase of Line No. 10, which crosses the city from the northwest to southeast, will open in June.

It cost 13 and half billion yuan, or around 1.8 billion US dollars, and has been shown off to the media as tests continue.

Zhou Zhengyu is Deputy Director of Beijing Municipal Committee of Communications.

"We have to build more subway lines to improve the subway network. To be specific, the three subway lines we are going to launch before the Olympics are mainly to serve the Olympic Games."

A short Olympic Line, which will serve many of the venues including the NATIONAL STADIUM, is still under construction.

It will run as a spur off line 10 and costs 300 million US dollars.

Line No. 4 will also open before the Olympics and will run north and south through west Beijing.

Line 5 opened last year, while an driver-less train serving Beijing's sprawling new international airport terminal will also be completed before the Olympics.

Beijing has 142 kilometres of subways and will have 200 when the Olympics open.

Further lines will open in the years ahead, as city officials try to encourage people to choose public transport over cars.