BEIJING, Sept. 9 (Xinhua) -- China's construction industry has seen rapid expansion since the country began to implement the reform and opening up policy in 1978, data showed.

The value-added output of the industry reached 5.57 trillion yuan (about 816.6 billion U.S. dollars) in 2017, compared with only about 13.9 billion yuan in 1978. The average annual growth rate was 16.6 percent, the National Bureau of Statistics (NBS) said at its website.

The value-added output of the industry accounted for 3.8 percent of the country's GDP in 1978, while the proportion rose to 6.7 percent in 2017, the NBS said.

The number of construction companies saw fast growth, reaching more than 300,000 last year. The private sector played a more important role, with the number of state-owned construction companies accounting for only 2.5 percent of the total in 2017, compared with more than 20 percent in 1996.

The companies contributed significantly to the country's infrastructure expansion. In 1978, China only had 52,000 km of railways in operation, while the length increased to 127,000 km by the end of 2017, including 25,000 km of high-speed railways, NBS data showed.