China stocks extended losses for a second straight session on Thursday, as a fresh dispute between Washington and Beijing over Hong Kong stoked concerns that an interim trade deal could be delayed.The blue-chip CSI300 index fell 0.5 per cent, to 3,889.60, while the Shanghai Composite index shed 0.3 per cent to 2,903.64.Completion of a "phase one" United States -China trade deal could be pushed into next year, trade experts and people close to the White House said, as Beijing presses for more extensive tariff rollbacks, and the Trump administration counters with heightened demands of its own.In a dinner speech in Beijing on Wednesday, Vice Premier Liu He said he was "cautiously optimistic" on a "phase one" deal, Bloomberg News said, citing people who attended the event ahead of a forum organised by Bloomberg LP.The crackdown on anti-government protests in Hong Kong may also complicate the completion of a deal.The Hong Kong issue is definitely a negative factor in the trade talks, Zhang Yansheng, principal researcher at the state-affiliated think-tank China Center for International Economic Exchanges, said at the Bloomberg forum.The United States House of Representatives on Wednesday passed two bills to back protesters in Hong Kong and send a warning to China about human rights, with President Donald Trump expected to sign them into law, while in the middle of trade negotiations with Beijing.Around the region, MSCI's Asia ex-Japan stock index was weaker by 1.12 per cent, while Japan's Nikkei index closed down 0.48 per cent.At 07:02 GMT, the yuan was quoted at 7.0407 per United States dollar, 0.06 per cent weaker than the previous close of 7.0364.As of 07:03 GMT, China's A-shares were trading at a premium of 28.06 per cent over the Hong Kong-listed H-shares.