Wall Street stocks opened sharply lower Monday, joining most international equity bourses in falling after US President Donald Trump launched trade wars against Canada, Mexico and China.
The tariffs, if maintained, are expected to prolong or worsen inflationary pressures, hitting growth.
About 25 minutes into trading, the Dow Jones industrial Average was down 1.4 percent at 43,904.26.
The broad-based S&P 500 fell 1.7 percent to 5,935.92, while the tech-rich Nasdaq Composite Index slumped 2.1 percent to 19,224.64.
"The quandary for the capital markets is figuring out if these tariff actions are a temporary negotiating tactic or a permanent feature," said Briefing.com analyst Patrick O'Hare.
Trump's tariff announcement has "ramped up a feeling of uncertainty that is weighing on market sentiment," O'Hare added.
Markets this week will be monitoring talks between Washington and counterparts in the three targeted countries.
Other key events include quarterly earnings from Google parent Alphabet, Ford and others, as well January US jobs data.