By Summer Zhen

HONG KONG, June 4 (Reuters) - China and Hong Kong stocks extended gains on Wednesday, supported by a rally in biotech and rare earth shares and hopes that a call between the U.S. and China would cool trade tensions.

** China's blue-chip CSI 300 Index .CSI300 climbed 0.5% by the lunch break, while the Shanghai Composite Index .SSEC rose 0.4%.

** Hong Kong benchmark Hang Seng .HSI was up 0.7% and the Hang Seng Tech .HSTECH rallied 1%.

** Hang Seng Healthcare Index .HSHCI jumped 3% to lead gains in Hong Kong, as investors bet on earnings growth in innovative drug makers.

** In A-shares, an index tracking shares of Hong Kong brokers .CSI399707 advanced 2.9% while CSI Rare Earth Industry Index .CSI930598 gained 2.3%.

** The export of rare earths has been thrust into the spotlight in the U.S.-China trade negotiations.

** Investor concerns over the latest U.S.-China dispute regarding access to chips and rare earths were slightly eased by the prospect of a possible call between U.S. President Donald Trump and Chinese leader Xi Jinping later this week.

** Trump has previously signaled that China's slow pace of easing the critical mineral export ban represents a violation of the Geneva agreement.

** Analysts say tariff uncertainties and U.S. debt issues will continue to roil markets.

** "(Trade) expectations are unstable, economic disturbances are still large, and the macro environment continues to be under pressure," analysts at Cinda Futures said in a note, expecting mainland A-shares to remain rangebound in the near term.

** The smaller Shenzhen index .SZSC was up 0.88%, the start-up board ChiNext Composite index .CNT was higher by 1.22% and Shanghai's tech-focused STAR50 index .STAR50 was up 0.57%​.

** Around the region, MSCI's Asia ex-Japan stock index .MIAPJ0000PUS was firmer by 0.90% while Japan's Nikkei index .N225 was up 0.84%.

(Reporting by Summer Zhen; Editing by Mrigank Dhaniwala)

((summer.zhen@thomsonreuters.com; 852-3462-7739;))