US stocks fell in early trade Monday after Greek voters rejected a creditor austerity package, throwing Greece and the eurozone into turmoil.
About 40 minutes into trade, the Dow Jones Industrial Average stood at 17,647.80, down 82.31 points (0.46 percent).
The broad-based S&P 500 fell 9.00 (0.43 percent) to 2,067.78, while the tech-rich Nasdaq Composite Index dropped 18.87 (0.38 percent) to 4,990.34.
Earlier, European bourses fell after 61 percent of Greeks voters opted against accepting further austerity measures to unlock key bailout funds.
The vote raised immediate worries about a cash crunch in Greece and the debt-wracked country's ability to stay in the eurozone.
"Statements from European officials about doing 'whatever is necessary' and actions to provide yet more liquidity as necessary may help, but the problems are real. Very real," said a note from Briefing.com.
"There is also now a serious risk that Spain and other countries will experience popular discontent towards austerity measures, spurred on by the undeniable resentment and anger represented in the Greek vote."
Most Asian markets finished lower after the Greek vote. Shanghai gained 2.41 percent as officials unveiled measures to shore up liquidity in Chinese markets.
Health insurer Humana gained 2.7 percent after unveiling a $37 billion deal to be acquired by rival Aetna. Aetna fell 4.6 percent.
Anthem and Cigna, two other health insurers that have been seen as possible merger partners, both fell. Anthem lost 1.8 percent, while Cigna fell 1.4 percent.
Weight Watchers surged 16.6 percent following a report in the New York Post that an activist hedge fund may lead a consortium of companies to buy out the weight-loss service.
Tech giants Intel and Cisco Systems fell 0.9 percent and 1.0 percent. Apple shed 0.7 percent.
Large banks were also weak, including Bank of America (-1.0 percent), Citigroup (-1.1 percent) and Wells Fargo (-0.9 percent).
Bond prices rose. The yield on the 10-year US Treasury fell to 2.31 percent from 2.38 percent Thursday, while the 30-year dropped to 3.11 percent from 3.19 percent. Bond prices and yields move inversely.