Asian markets resumed their downward spiral Thursday after Federal Reserve boss Janet Yellen sounded a warning over a possible British exit from the EU, while investors prepare for a keenly awaited Japanese central bank policy decision.

After a two-day meeting the Fed lowered its growth forecasts for this year and the following two, and flagged interest rates rises to be lower and slower, highlighting increasing concern about the US and global economic outlook.

Her comments dragged New York stocks lower and sent the dollar tumbling against the yen and even the British pound despite fears of Britain leaving the EU.

In a news conference after the Fed kept interest rates unchanged, Yellen voiced confidence in the US economy but said there were concerns about the impact a British exit would have across the world.

"Clearly, this is very important decision for the United Kingdom and for Europe," she told reporters.

"It is a decision that could have consequences for economic and financial conditions in global financial markets. If it does so, it could have consequences in turn for the US economic outlook."
Japan's Nikkei index was down 1.1 percent by the break as the yen strengthened further against the dollar, with traders expecting the Bank of Japan to hold off unveiling any fresh stimulus after its own policy meeting Thursday.

Hong Kong was down 1.7 percent and Shanghai lost 0.2 percent. Seoul shed 0.5 percent and Singapore 0.6 percent. However, Sydney added 0.4 percent.

World markets have been in turmoil over the past week on worries about the global economic outlook and, in recent days, a growing sense that the June 23 referendum will see Britons vote to break away from the European Union.

Despite jitters over next week's vote the pound held most of its gains against the dollar Thursday morning, sitting at 1.4201 having fallen to a two-month low below $1.41 earlier in the week.

Oil prices extended their losses as unrest in Nigeria and wildfires in Canada, which had helped limit output, begin to ease.

US benchmark West Texas Intermediate was down one percent at $47.52 and Brent shed 0.8 percent to $48.56.

WTI is down eight percent from last week's 11-month high, while Brent has lost 6.6 percent from an eight-month peak.

- Key figures around 0230 GMT -

Tokyo - Nikkei 225: DOWN 1.1 percent at 15744.80 (break)

Shanghai - Composite: DOWN 0.2 percent at 2,881.28

Hong Kong - Hang Seng: DOWN 1.7 percent at 20,113.43

Euro/dollar: UP at $1.1272 from $1.1263 late Wednesday

Pound/dollar: DOWN at $1.4200 from $1.4212

Dollar/yen: DOWN at 105.66 yen from 105.98 yen

New York - DOW: DOWN 0.2 percent at 17,640.17 (close)

London - FTSE 100: UP 0.7 percent at 5,966.80 (close)