Global shares tumbled after a Wall Street sell-off triggered by concerns over artificial intelligence stock valuations. Japan's Nikkei and South Korea's Kospi plunged 6 per cent, while European markets also declined amid growing uncertainty over the technology sector. Tokyo: Global shares tumbled on Friday following a broad sell-off on Wall Street in shares of companies related to artificial intelligence. France's CAC 40 shed 1.1 per cent in early trading to 8,117.