Investors are bidding up U.S. stocks on bets that lower taxes under the Trump administration will boost corporate profits, but they may be getting overly complacent about risks, a U.S. central banker said in an interview.

"The stock market seems to be running pretty much on fumes," San Francisco Federal Reserve Bank President John Williams said in an interview carried on Sydney's ABC News affiliate and available on the internet on Tuesday. "It's something that clearly is a risk to the U.S. economy, some correction there -- it's something we have to be prepared for to respond to if it does happen."

Williams, who is giving a series of talks in Australia, said that for his part he doesn't believe any Trump fiscal policies will begin to affect the economy until 2018 or 2019.

U.S. stock-market indexes have set records this year, driven by a 19-percent climb in the technology index. Williams said he does not see the U.S. heading for a dot-com style crash like the late 1990s, because unlike then, the rise in stocks is being driven by a fundamentally sound U.S. economy.

Still, with measures of market volatility near historic lows, "I am somewhat concerned about the complacency in the market," he said.