New Delhi, Oct. 27 -- While global tech stocks teeter, in China they have already crashed as lofty valuations collapse under worries about AI demand and curbs on Chinese exports.

The meltdown, tanking the mainland STAR50 index, opens new tab of AI and semiconductor leaders ​by 40% in less than four months and vaporising some $480 billion in market value, is an ill omen for wobbly world markets and a dampener on China's efforts ‌at encouraging its savers into stocks to fund the AI boom.

It has also slammed the brakes on a rally running two years, since economic stimulus promises sent shares soaring, and has stalled Beijing's push to break with a long boom-bust pattern and drive a "slow bull" market that delivers reliable perf...