The Dow led the declines in the US, falling more than 4%, while the S&P 500 and Nasdaq dropped more than 3%.
The FTSE 100 index of top UK firms fell more than 3%, with aerospace, travel and housing firm among the hardest hit.
The pound meanwhile fell to its lowest level against the dollar in over three decades, trading at $1.18.
The US on Tuesday outlined a $1tn (£830bn) package to support the world’s biggest economy.
UK chancellor Rishi Sunak also revealed a £350bn stimulus package for UK firms, including £330bn of business loan guarantees.
It also included aid to cover a business rates holiday and grants for retailers and pubs. Help for airlines is also being considered.
Mr Sunak told a news conference: “Never in peacetime have we faced an economic fight like this one.”
The stimulus measures taken globally also failed to buoy Asian stocks. Japan’s benchmark Nikkei 225 ended Wednesday 1.7% lower, the Hang Seng in Hong Kong fell by 3.3%, and China’s Shanghai Composite lost 1.8%.
2008 financial crisis is nothing compared to this
On Tuesday, US Treasury Secretary Steven Mnuchin said he supports sending money directly to Americans as part of a $1tn stimulus plan aimed at averting an economic crisis caused by the virus.
The overall aid package would be larger than the US response to the 2008 financial crisis, amounting to nearly a quarter of what the US federal government spent last year.
In Japan Prime Minister Shinzo Abe is reportedly forming a panel of key economic ministers and Bank of Japan Governor Haruhiko Kuroda to discuss measures to prop up the economy.
The move, which would bring Japan in line with other nations, is designed to avert an economic crisis in the country, which some fear could tip into recession.