Waves of selling battered stock indexes Monday amid trade tension and escalating Hong Kong protests. 

The Dow Jones Industrial Average fell 391 points, or 1.49%, to 25,896.44, while the S&P 500 shed 1.23% to 2,882.69 and the Nasdaq Composite declined 1.2% to 7,863.41. The benchmark 10-year Treasury yield, which last week fell to its lowest since 2016, dropped 1.63%.

The plunge comes one week after stock averages suffered their worst trading day since December with trade threats between the U.S. and China continuing to stoke fears of an economic slowdown. President Trump on Friday suggested to reporters that a trade meeting next month with China may not take place.

Meanwhile, anti-government protests in Hong Kong intensified Monday, as roughly 5,000 protesters flooded Hong Kong International Airport. 

"Hong Kong has kind of been under the radar of most traders... but increasingly I feel that this has the potential to spiral into a bigger market worry. Today's moves highlight the risks," Neil Wilson, chief analyst at traders Markets.com, told Agence France-Presse.

Among the biggest stock-market decliners Monday were Disney (DIS), which fell 2.78% and Goldman Sachs (GS) dropped 2.61%. Among other decliners, were Facebook (FB), which dropped 1.32%, Amazon (AMZN), which fell 1.25%, Alphabet (GOOG), which saw a loss of 1.12%, and Apple (AAPL), which dipped 0.25%.

Merck (MRK) was the only Dow 30 company to post a gain Monday, with its price of shares jumping 0.22%.