Investor anxiety deepened Friday as a familiar medley of fresh lows in oil prices, stumbling Chinese stocks and weak U.S. economic data sent the Dow Jones Industrial Average to its biggest one-day percentage drop since early September.

The Dow industrials lost almost 400 points in Friday’s selloff, and investors snatched up bonds anew, sending 10-year Treasury yields briefly below 2% for the first time since October. Among the economic reports Friday, U.S. retail sales showed their weakest year for growth since the end of the recession in 2009, while a regional manufacturing survey disappointed.

Further complicating Friday’s action, investors were concerned about holding stocks heading into a three-day holiday weekend in the U.S.

The domestic stock market will be closed Monday. Others around the world, including Chinese markets, are open and could fall even further.

Financial adviser Michael Fein said he received the most phone calls from nervous clients ever on Friday morning. One client even dropped into Mr. Fein’s office to gauge whether she should be panicking.