A top Federal Reserve official sees fresh signs of a US housing bubble and has warned about the central bank's ongoing purchases of mortgage-based bonds. "I'm beginning to see signs across the country that we are entering, once again, a housing bubble," Dallas Fed president Richard Fisher said. "So that leads me ... to be very cautious about our mortgage-backed securities purchase programme." A mortgage-market bubble in part caused the 2007-2009 financial crisis from which the world's largest economy is still recovering. In response, the Fed has depressed interest rates and is buying US$85 billion in assets each month, including US$40 billion in mortgage-backed securities. Fisher, a vocal hawk on monetary policy, repeated he would not support a reduction in the quantitative easing programme at a Fed meeting this month, in large part because of the fiscal "mess" in Washington. But citing rising year-on-year house prices, he warned that the Fed's hyper-accommodative policies could be inflating dangerous asset-price bubbles. Home resales rose in August and median prices were up 14.7 per cent over the previous 12 months, according to the National Association of Realtors, although other data have suggested a sharp rise in mortgage rates has dented the housing recovery. "We have to be watchful and realise there has historically been an era of the Fed over-stimulating" since the Great Depression, Fisher said. "I worry we are following that tradition now. No one knows when the bubble pops. But I would argue that ... with each dollar we buy in Treasuries and mortgage-backed securities, we're getting closer to the tipping point."