By Agence France-Presse
The Dow Jones Industrial Average finished with a loss of 1.8 percent or more than 400 points, at 22,445.37, taking losses for the week to nearly seven percent.
The broad-based S&P 500 slumped 2.1 percent to 2,416.58, while the tech-rich Nasdaq Composite Index slid 3.0 percent to close at 6,332.99. The declines pushed the Nasdaq into a "bear" market, meaning a retreat of 20 percent from its peak.
The losses came as Washington teetered towards a likely government shutdown as US President Donald Trump dug in on threats to close the government if congressional Democrats continue to refuse his demand for funds to build a wall on the border of Mexico.
Thousands of US government employees could be furloughed right before the end-of-year holidays without a paycheck if Trump and congressional Democrats fail to strike a deal by midnight (0500 GMT).
With that deadline looming, investors received another jolt in the final hour of trading when White House advisor Peter Navarro delivered hardline comments on the ongoing trade talks with China.
"China is basically trying to steal the future of Japan, the US and Europe, by going after our technology," Navarro, a longtime China hawk, told the Japan's Nikkei news agency in an interview conducted Thursday but published Friday.
And he said China must address all US concerns about its trade policies, saying there are "no half-measures."
Investors also have been anxious over the surprise resignation of Defense Secretary Jim Mattis, who laid out significant policy disagreements with the US president in his letter to Trump which he made public.
"We are in a fragile environment," said Gregori Volokhine of Meeschaert Financial Services.
"The extremist position is winning in the Trump administration, not just on trade but on everything."
Besides worries over the US-China trade war and a possible government shutdown, investors have been unnerved by the Federal Reserve's decision to raise interest rates this week, and projecting it would continue to raise next year.
New York Federal Reserve Bank President John Williams on Friday opened the door to a more benign monetary policy in 2019, saying the Fed was listening to the fears about the risks and will "be ready to reassess and re-evaluate our views and our policy stance."
Stocks briefly rallied on Williams remarks, but fell quickly back into the red.