The Nikkei 225 has plunged over 1% following a promising start, which only lasted just under 30m, time sellers needed to match all the initial demand and overwhelm early attempts to recover the critical 16,000 area with strong supply, with the topside failure at 16,050 POC leading to a sharp fall towards day lows near 15,800.Risk off / supply on the riseIn related markets, the US 30 year Treasury yield continues to edge lower, as the flight to safety keeps the long-end of the US bonds very well bid. Meanwhile, Gold continues to find steady demand, last at 1,285.00, reinforcing the sense of risk aversion. Copper has also seen a collapse in prices in the last few minutes, despite a weaker USD in Asia, suggesting that the supply environment is quite strong.Brexit fears impacting global marketsThe main driver behind the current depressed mood in markets in the possibility of an exit as member of the EU by the UK on its June 23th referendum, with polls showing the 'Leave' campaign taking a lead that can no longer be ignored. As Greg Gibbs, Founder at Amp GFX notes: "As the UK romances the idea of Brexit, the global financial markets, world leaders and policymakers are watching on in amazement that it would consider such a risky move. It is fair to say we are all transfixed and no decisions will be made until we know the outcome. Markets are likely to be frozen in time, or gyrating on voting opinion polls. Even the FOMC and BoJ policymakers are likely to tread much more carefully in their policy deliberations this week, preferring to wait out the 23 June referendum."