Nikkei tumbles 5.1% as Asian markets extend rout

CNBC reports:

Markets in Asia dropped on Friday, with the Nikkei tumbling, after a sell-off on Wall Street as oil remained volatile and concerns about how central banks' easing measures will affect banks' earnings persisted.

"The idea that central banks are now fully targeting the interest rate structure and putting a gun to domestic banks heads in a fight to stoke credit growth is in no way an equity friendly story," wrote Chris Weston, chief market strategist at spreadbetter IG, in a morning note. The Bank of Japan blindsided markets on January 29 by cutting its benchmark rate into negative territory in a move that's likely to weigh on banks' earnings.

Grim.