Stock markets extended a global sell-off Tuesday as traders appeared increasingly nervous about the prospect of Britain voting to leave the European Union next week.

The pound and euro both fell and gold prices edged higher amid a flight to safety.

And worried investors for the first time accepted negative yields for the privilege of owning rock-solid German government bonds.

"That's really a flight to safety in front of what could be a destabilizing event if the vote goes to leave the EU," said Art Hogan of Wunderlich Securities.

European markets fell sharply, led by Paris, down 2.3 percent, and London, where the FTSE 100 fell 2.0 percent.

US share losses were more modest, the S&P 500 giving up 0.2 percent.

The euro fell to $1.1208 and hit a three and a half year low against the yen before pulling back to 118.92 yen.

- Brexit 'Leave' camp leading -

With just over a week to go until Britain's referendum, a series of polls have put the "Leave" camp in front, raising the possibility that its four-decade ties to the European bloc could be cut.

The prospect of one of the biggest economies in the EU breaking away has led to warnings of a new wave of world market turmoil as they struggle to recover from the panic that wiped trillions off valuations at the start of the year.

Caution across markets was reinforced by policy meetings of the British, Japanese and US central banks taking place this week.

The US Federal Reserve is not expected to hike interest rates on Wednesday, but investors will be watching to see if it turns more dovish amid heightened market uncertainties and weak inflation.
On Thursday the Bank of Japan could possibly expand its asset purchases to further boost the struggling Japanese economy.

Also meeting on Thursday, the Bank of England will almost certainly keep policy on hold ahead of the June 23 Brexit referendum.

But the minutes to its last meeting could show the level of concern and preparation if the vote favors breaking with the European Union.

"Expectations of weak global growth and ever-enduring easy monetary policy, likely to be reinforced at central bank meetings this week, is seeing a mass exit from equities and feeding demand for bonds, sending yields to record lows," said Jasper Lawler, analyst at traders CMC Markets.

- Key figures at 2100 GMT -

New York - DOW: DOWN 0.3 percent at 17,674.82 (close)

New York - S&P 500: DOWN 0.2 percent at 2,075.32 (close)

New York - Nasdaq: DOWN 0.1 percent at 4,843.55 (close)

London - FTSE 100: DOWN 2.0 percent at 5,923.53 points (close)

Frankfurt - DAX 30: DOWN 1.4 percent at 9,519.20 points (close)

Paris - CAC 40: DOWN 2.3 percent at 4,130.33 points (close) 

EURO STOXX 50: DOWN 2.0 percent at 2,797.18 points (close)

Tokyo - Nikkei 225: DOWN 1.0 percent at 15,859.00 (close)

Hong Kong - Hang Seng: DOWN 0.6 percent at 20,387.53 (close)

Shanghai - Composite: UP 0.3 percent at 2,842.19 (close)

Euro/dollar: DOWN at $1.1208 from $1.1292 late Monday

Dollar/yen: DOWN at 106.11 yen from 106.19 yen

Pound/dollar: DOWN at $1.4118 from $1.4245