The Nikkei share average shed 3.6 percent to end the day at 16,164.16, its lowest close since March 1. Japan's benchmark index ended the week 4.9 percent lower.
The Nikkei Volatility Index climbed as much as 27 percent during the session, its highest in more than two weeks.
Hong Kong's benchmark index suffered its biggest one-day loss in five weeks on Friday, after rating agency Standard & Poor's downgraded its outlook for China and Hong Kong.
The Hang Seng index fell 1.3 percent, to 20,498.92, its biggest one-day percentage loss since Feb. 25. For the week, the Hang Seng was up 0.8 percent.
The China Enterprises Index lost 1.8 percent on Friday, to 8,842.86 points. For the week, it gained 1.6 percent.
S&P on Thursday cut its outlook for China's sovereign credit rating to negative from stable, and also downgraded the outlook for Hong Kong.
China stocks recovered from early losses and ended Friday roughly flat, as investors weighed the impact from Standard & Poor's downgrade of China's credit outlook and a surprise pick-up in March manufacturing activity.
China's blue-chip CSI300 index rose 0.1 percent, to 3,221.89, while the Shanghai Composite Index gained 0.2 percent, to 3,009.53 points.
For the week, CSI300 was up 0.8 pct while the SSEC was 1 percent higher.
Late on Thursday, rating agency S&P downgraded its outlook for China's sovereign credit rating to negative from stable, saying the government's reform agenda is on track but likely to proceed more slowly than expected.
Reference: Reuters
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