China's economy expanded at 6.5 percent during the July-September period on the year, its worst pace in more than nine years amid a tit-for-tat tariff escalation with the United States, official data showed Friday.

Although the headline figure was in line with the government's target of around 6.5 percent for the year, it was down from the 6.7 percent growth in gross domestic product in the second quarter of this year.

The latest GDP data comes as fears continue to mount that the world's second-biggest economy will be weighed down by its intensifying trade war with the United States, which has imposed higher tariffs on a wide range of imports from China.

China's economic expansion decelerated for the second straight quarter. The 6.5 percent rise was the weakest since the January-March period in 2009, when the growth rate was 6.4 percent as the world economy suffered from the aftermath of the 2008 global financial crisis.

"The economy continued to stay stable with good growing momentum," the Chinese National Bureau of Statistics said.

But China "must be fully aware that challenges from outside are increasing," the bureau said. "There are uncertainties behind the stable economy that is also growing more slowly and under greater downward pressure."

China should "deepen" its reform and opening-up policy, the bureau said, apparently seeking to draw a contrast with U.S. President Donald Trump's "America First" stance promoting trade protectionism.

Analysts say China is expected to lose growth momentum further, as prices of the country's products will be jacked up in the United States, the world's largest market, choking exports -- a major driver of the Chinese economy.

A possible economic slowdown is also likely to prevent the Chinese leadership, led by President Xi Jinping, from achieving its goal of building a "moderately prosperous society," defined by Beijing as doubling its 2010 GDP and per capita income by 2020.

Friday's data showed China's economy grew 6.7 percent on year to 65.09 trillion yuan ($9.38 trillion) in the first three quarters of 2018. Growth of investment and retail sales, however, slowed as domestic demand has become sluggish.

Investment in fixed assets, which includes spending on property construction and infrastructure, rose 5.4 percent in the nine months of this year, 0.6 percentage point lower than the first six months.

During the same period, growth in retail sales of consumer goods climbed 9.3 percent, down from 9.4 percent in the first half of 2018.

The total value of exports increased 6.5 percent in the nine months from January, but many economists are skeptical about whether China's shipments will continue to grow down the road.

Last month, Washington invoked tariffs on an additional $200 billion in Chinese imports. With this third round of tariffs, the United States is now imposing double-digit tariffs on around half of the products it imports from China each year.

China immediately took retaliatory action, slapping additional tariffs on $60 billion in U.S. imports, which means Beijing has so far levied tariffs on more than 80 percent of all goods imported from the United States.

To realize the "moderately prosperous society," where all citizens can enjoy comfortable lives, China's economy needs to expand at an average annual rate of around 6.5 percent.

China's leadership previously put more emphasis on structural reforms and monetary tightening than on economic growth in an attempt to curtail corporate debt expansion and avoid a bursting of asset-inflated bubbles at home.

Recently, a heightening trade spat has been fanning concern that China's export-oriented economy would grow at a substantially slower rate than had been expected, prompting the country's authorities to take economic stimulus measures.

Cutting interest rates and boosting public spending would allow many companies to borrow money and invest in fixed assets, but make it more difficult for the Chinese government to normalize the financial system.

The International Monetary Fund forecast earlier this month that China's economy will grow 6.2 percent this year, down 0.2 percentage point from its estimate in July.

Stock prices have also been on a downward trend since Trump started to wage a trade war in a bid to curb the huge U.S. trade deficit with China, leaving financial market participants pessimistic about the outlook for the Chinese economy.

On Thursday, the benchmark Shanghai Composite index closed down 2.9 percent at 2,486.42, after falling to its lowest point since November 2014 in the morning.