Japan's benchmark Nikkei 225 Stock Average tumbled 5 per cent into a bear market on Christmas Day as the global equity rout continued unabated in the last week of the year, with renewed turmoil in Washington rattling investors.

Tuesday's selloff took its cue from the S&P 500's worst-ever trading session before the Christmas holiday. Shares in China, the other major Asian market open on Tuesday, also declined as investors shrugged off a pledge by the government to do more to support companies.

A man looks at an electronic stock board outside a securities firm in Tokyo. The Nikkei 225 index entered bear market territory, as Japanese stocks headed for their worst December on record. Credit:Bloomberg

Investors got mixed signals from Washington heading into the resumption of US stock futures trading at 6 pm New York time. President Donald Trump said a partial US government shutdown will continue until funding for a US-Mexico border wall is secure.

He expressed confidence in his Treasury secretary and the Federal Reserve even as he again criticised the central bank for raising rates too quickly.