Chinese economic growth decelerated to the 25-year low of 6.9 percent in 2015, down from 7.3 percent in 2014, according to data released Tuesday by the National Bureau of Statistics.

The GDP growth rate was reported as 6.8 percent in the fourth quarter, down from 6.9 percent in the third and 7 percent in the first two quarters last year.

The growth rate is still within a reasonable range as it achieved the government's annual growth target, described as "around 7 percent", said economists.

The service industry, for the first time in history, contributed more than a half of the total GDP growth, or 50.5 percent, suggesting a deepened restructuring of the growth pattern, according to the NBS.

Export and industry, particularly heavy industry, are no longer main engines to drive the nation's growth, while government-led investment in public infrastructure, manufacturing of more highly value-added electronic systems, and e-commerce are new leaders of the economy.

Meanwhile, the manufacturing industry accounted for 40.5 percent of the GDP growth while 9 percent growth came from the agricultural industry.

The industrial output growth retreated to 6.1 percent last year from 8.3 percent in 2014, hitting the lowest level since the global financial crisis.

Fixed-asset investment increased by 10 percent, a sharp decrease from 15.7 percent in 2014.

Retail sales moderated to 10.7 percent from 12 percent, the NBS showed.

Despite the growth slowdown, the increase in the employed population and per capital income remained stable. In 2015, 6.8 million new jobs were created in the country. The per capita income reached by 8.9 percent nominally to 21,966 yuan ($3,341).

John Zhu, a senior economist in China at HSBC Holdings, said that sustained long-run GDP growth in China, which needs to further rebalance the industrial structure, will depend on supply-side factors and labor productivity.

"The recent rise of the services sector to more than half of GDP has led some to celebrate a new kind of rebalancing on the output side," he said. "A very high saving rate in the country allows for higher investment in raising the capital stock and sustains growth in labor productivity. Given China's current stage of development, more investment will be needed, not less."

In the first half of January, volatility escalated in both the Chinese equity and foreign exchange markets, due to concerns about the world's second largest economy's ability to successfully rebalance its economy.

Chang Jian, chief economist in China at Barkley's Capital, expected more easing measures on both the monetary and fiscal fronts, given the weakening outlook.

"On monetary policy, we look for two benchmark rate cuts by 25 basis points each and two cuts of reserved requirement ratio in the first half to support liquidity and lending. We expect more targeted fiscal stimulus announcements to support consumption and infrastructure investment, as well as more reductions in corporate taxes and fees," Chang said.