Mainland and Hong Kong stocks fell in opening trades on Friday as stocks tracked an overnight decline in US peers on stretched valuation concerns.

The Hang Seng Index opened down 135 points, or 0.51 percent, at 26,350.

Up north, the benchmark Shanghai Composite Index was 0.34 percent at 3,994, the Shenzhen Component Index was 0.54 percent lower at 13,380 while the ChiNext Index, which tracks China's Nasdaq-style board of growth enterprises, was down 0.72 percent at 3,201.

In Japan, the Nikkei share average fell as it heads for its biggest weekly drop since early April.

The tech-heavy Nikkei slid as much as two percent and was last down 1.8 percent at 49,955, slipping below the psychologically key 50,000 mark.

Startup investor SoftBank Group dropped 8.4 percent and chip-testing equipment maker Advantest, a Nvidia supplier, slumped seven percent, making them the Nikkei's top two decliners in index-point terms.

The broader Topix lost 0.8 percent to 3,286.

South Korean shares too fell and, pretty much like in Japan, were headed for their first weekly decline after five straight weeks of gains.

The benchmark Kospi was down 34 points, or 0.85 percent, at 3,994 at midday.