Hong Kong (CNN Business) China's economic slowdown is deepening as its trade war with the United States gets worse.

The world's second biggest economy grew 6.5% in the third quarter of this year, according to official data published Friday. That's its weakest quarterly growth since the depths of the global financial crisis in early 2009 and below economists' expectations of 6.6%.

The Chinese economy has lost momentum this year following government efforts to try to rein in high levels of debt. It has also started coming under pressure from US tariffs on more than $250 billion of its exports.

"We think more easing will still be needed in order to stabilize growth," Julian Evans-Pritchard, senior China economist at research firm Capital Economics, said in a note to clients Friday. He predicts the slowdown will bottom out around the middle of next year.

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