Mainland China and Hong Kong shares opened on Wednesday mixed as US President Donald Trump added tariff threats on copper and pharmaceuticals to his broadening trade agenda.

Trump announced plans for a 50 percent duty on copper imports and a potential 200 percent levy on pharmaceuticals a day after the White House sent letters to Japan, South Korea and other countries about tariffs to kick in August 1.

In Hong Kong, the benchmark Hang Seng Index lost 86 points, or 0.36 percent, to open at 24,061.

On the mainland, stocks opened higher, with the benchmark Shanghai Composite Index up 0.04 percent to open at 3,498 while the Shenzhen Component Index opened 0.04 percent higher at 10,592.

The ChiNext Index, tracking China's Nasdaq-style board of growth enterprises, was down 0.08 percent to open at 2,179.

In Seoul, shares rose for a third straight session as financial stocks rallied on policy hopes while the broader market's focus was on US tariffs and domestic monetary policy.

The benchmark Kospi was up 15 points, or 0.5 percent, at 3,130, as of midday.

In Sydney, shares fell, led by losses in gold and mining stocks on Trump's threats on copper and pharma levies.

The S&P/ASX 200 index fell 0.7 percent to 8,535 by midday. (Xinhua/Agencies)