The S&P 500 and the Nasdaq touched record highs for the second straight day on Tuesday following a spate of upbeat corporate earnings, while Emmanuel Macron's victory in the French presidential election improved risk appetite.
The VIX, Wall Street's "fear gauge", hit its lowest level in more than a decade earlier in the day. A lower VIX typically indicates a bullish outlook for stocks.
The 10-year US Treasury yield rose to its highest in a month, while gold prices fell, indicating a shift in investor preference for riskier assets.
However, analysts cautioned against investor complacency, especially after the market's strong run since Donald Trump's elections as US president.
"In the short-term, investors can enjoy this run, but they should start to hedge their positions and look for safety," said Christian Magoon, chief executive at Amplify ETFs in Chicago, Illinois.
"Given world events, common sense would say there should be at least average volatility in daily price movement on the S&P 500. The index seems to be very lethargic."
The index has not moved more than 0.4 per cent in either direction in the past 11 trading days.
At 11:03 am ET the Dow Jones Industrial Average was up 8.97 points, or 0.04 per cent, at 21,021.25, the S&P 500 was up 2.03 points, or 0.08 per cent, at 2,401.41 and the Nasdaq Composite was up 23.57 points, or 0.39 per cent, at 6,126.23.
Five of the 11 major S&P sectors were higher, while the typically defensive plays such as utilities and telecom services fell.
Shares of Valeant Pharmaceuticals jumped more than 16 per cent after the company posted its first profit in six quarters.
Endo International, Office Depot and Marriott also rose after reporting better-than-expected quarterly earnings.
Wayfair surged to an all-time high of $62.65 after the online furniture retailer revenue beat analysts' expectations.
Declining issues outnumbered advancers on the NYSE by 1,462 to 1,304. On the Nasdaq, 1,439 issues rose and 1,214 fell.