SHANGHAI, May 29 (Reuters) - Mainland China and Hong Kong stocks advanced on Thursday as sentiment improved after a U.S. trade court blocked President Donald Trump's so-called reciprocal tariffs that had weighed on global trade and roiled financial markets.

Key Chinese stock indexes rebounded and looked set to snap their five-day losing streak, while the U.S. dollar rallied and gold sank in overseas market, as risk appetite sharply changed following the court decision. FRX/

** A U.S. trade court blocked President Donald Trump's tariffs from going into effect in a sweeping ruling on Wednesday that found the president overstepped his authority by imposing across-the-board duties on imports from U.S. trading partners.

** At the midday break, the Shanghai Composite index .SSEC was up 0.72% at 3,363.97 points, while the blue-chip CSI300 index .CSI300 was up 0.68% 3,862.44 points. If both indexes retain all the gains at the close, they will post their first daily gain since May 21.

** The smaller Shenzhen index .SZSC was up 1.23%, the start-up board ChiNext Composite index .CNT was higher by 1.16% and Shanghai's tech-focused STAR50 index .STAR50 was up 1.25%​.

** In Hong Kong, the benchmark Hang Seng Index .HSI was up 0.65% at 23,408.36 points, while the Chinese H-share index listed in the financial hub, the Hang Seng China Enterprises Index .HSCE rose 0.68% to 8,501.15 points.

** Around the region, MSCI's Asia ex-Japan stock index .MIAPJ0000PUS was firmer by 0.41% while Japan's Nikkei index .N225 was up 1.58%.

** However, gains in Chinese shares were capped as uncertainty around bilateral relations between Washington and Beijing still lingered, traders and analysts said.

** "The ruling gives an interim boost to risk sentiment which saw equity futures, bond yields and the dollar higher," said Frances Cheung, head of FX and rates strategy at OCBC Bank.

"Development on tariff and trade relation remains fluid. Investors may be reluctant to load heavy positions on either side of the trade."

** The U.S. has ordered companies that offer software used to design semiconductors to stop selling to China without first getting an export license, sources told Reuters.

** However, Beijing-based Empyrean Technology Co 301269.SZ, which is considered to be China's primary alternative to the U.S. giants like Cadence, Synopsys, and Siemens in the electronic design automation (EDA) market, jumped 11.9% in morning deals.

** U.S. Secretary of State Marco Rubio announced on Wednesday the United States will start "aggressively" revoking visas of Chinese students, including those with connections to the Chinese Communist Party or studying in critical fields.

(Reporting by Shanghai Newsroom)