The optimism that greeted Federal Reserve boss Jerome Powell's indication on Wednesday that borrowing costs could be cut in September has given way to trepidation that the slowdown in the world's number one economy might be picking up too much speed.

The central bank has for months been looking for confirmation that inflation is well on the way down and the labour market is softening, while at the same time trying to avoid a sharp plunge in business activity. It has largely been confident of achieving a "soft landing".

But news Thursday that the US factory sector shrunk faster than forecast in July -- and for the fourth consecutive month -- raised eyebrows.

That came as another report showed the private sector created far fewer jobs than expected in July and a lot less than June.

The private sector added 122,000 jobs in July, down from June's revised 155,000 figure and marking a weaker performance than anticipated, while unemployment claims also spiked more than thought.

Focus is now on the release of the major jobs report due later Friday, which will give a clearer snapshot of the labour situation.

The news dealt a blow to investors, who are also dealing with a disappointing earnings season from Big Tech, a key driver of the global rally that has helped push many markets to multiple record highs this year.

US chip titan Intel became the latest bearer of bad news, warning it would slash more than 15 percent -- about 18,000 -- of its workforce as it streamlines operations. The firm reported a loss of $1.6 billion in the recently ended quarter and said the third quarter would also disappoint.

Microsoft, Amazon, Tesla and Google-parent Alphabet have also fallen short of hopes, and while Apple beat forecasts, talk is now growing that the valuations of some of these market darlings may be too high and in need of a pullback.

All three main indexes tumbled in New York, with the Nasdaq more than 2 percent off.

And Asia fared just as poorly, with Tokyo the standout.

The Nikkei 225 tanked more than 5 percent at one point owing to a stronger yen, which hits Japan's key export sector.

The country's tech giants were also hammered as they took the lead from losses by their US counterparts, with chip titan Tokyo Electron losing 10 percent and Sony shedding more than 6 percent.

Daiwa Securities said in a note: "Following falls in New York stocks, the BoJ's additional rate hike, and the yen's further appreciation, market sentiment is rapidly cooling down."

Hong Kong and Sydney were off more than 2 percent, while Seoul and Taipei shed more than 2 percent, with losses also in Shanghai, Wellington, Manila, Singapore and Jakarta.

Wednesday's decision by the Bank of Japan to hike interest rates for the second time in 17 years -- and talk of another to come -- strengthened the yen to as much as 148.51 per dollar, its best level since March.

That is just weeks after hitting nearly 126 at the start of July, its weakest in almost four decades.

The pound extended losses against the greenback, a day after the Bank of England cut its main interest rate for the first time since the COVID pandemic broke out in 2020.