The growth was in line with the government's annual target of 6-6.5 percent set for 2019.
In the third quarter, the country's GDP rose 6 percent year on year, according to the NBS data.
The Chinese economy has maintained overall stability, the statistical authority said at a press conference, while acknowledging that China faces downward pressure amid slower global economic growth and more external uncertainties.
A breakdown of the data showed output of the service sector, which accounted for 54 percent of the total GDP, rose 7 percent in the first three quarters of the year, outpacing a 2.9-percent increase in the primary industry and a 5.6-percent rise in the secondary industry.
Consumption continued to be the mainstay in driving up demand, with the final consumption contributing 60.5 percent to the economic growth in the Jan.-Sept. period, NBS data showed.