Technology companies led sell-offs on stock markets Wednesday, as investors grow increasingly worried about an AI bubble following a rally that has propelled valuations to record highs.

Sentiment was hit also by the US government shutdown, which Wednesday became the longest ever, topping the 35-day record set during President Donald Trump's first term in office, as his administration warned of holiday air travel chaos and threatened Americans' benefits in a bid to force a resolution.

A total 1.4 million federal workers, from air traffic controllers to park wardens, are on enforced leave or working without pay.

"As well as valuation fears, the US is grappling with a nation in shutdown," noted Emma Wall, chief investment strategist at Hargreaves Lansdown.

"The US is nearing peak travel p

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