A brutal stock market sell-off intensified on Monday as investors saw few signs that US President Donald Trump would back down from his sweeping tariff plans , and foreign nations prepared to retaliate.

US stocks were opened sharply lower for a third day on Monday after heavy losses at the end of last week. The S&P 500 was nearing a bear market after the Nasdaq 100 closed in bear market territory last Friday.

Here's where US indexes stood shortly after the 9:30 a.m. opening bell on Monday:

S&P 500: 4,906.75, down 3.3%

Dow Jones Industrial Average: 37,124.58, down, 2.87% (-1,097.58 points)

Nasdaq Composite: 14,971.08, down 4%

European stocks tumbled in morning trading, and Asian markets started the week deep in the red as investors fretted over the impact of Trump's tariffs on company earnings and economies.

Germany's DAX fell more than 6% before making up some ground in afternoon trading. Britain's FTSE 100 was down 3.4%, France's CAC 40 was 3.7% lower, and the broad Euro Stoxx 600 index dropped 4%.

The MSCI Asia Pacific Index slumped the most since the 2008 financial crisis, according to Bloomberg's analysis.

"The impact spans economies, financial markets, supply chains, and geopolitics and will force governments, businesses, and households to retune their approach to trade relations, capital expenditure, and consumption," wrote Eunice Tan, a S&P Global Rating credit analyst, on Monday.

JPMorgan CEO Jamie Dimon advocated for free and fair trade and support for American workers displaced by outsourcing in his annual letter to shareholders on Monday. But the billionaire banker also predicted the tariffs would cause higher inflation and slower growth in the short term, and could spark retaliation, hurt confidence, deter foreign investment in the US, erode corporate profits, and weaken the US dollar.

Trump sounded defiant in a Truth Social post on Monday, writing that oil and food prices are down and "there is NO INFLATION." He also wrote that "the long time abused USA is bringing in Billions of Dollars a week from the abusing countries on Tariffs that are already in place."

Asia markets saw major losses across countries, including China and Hong Kong, which were closed on Friday for a holiday. Shares in chip hub Taiwan — which was hit with a 32% tariff rate — tanked nearly 10% in its biggest decline on record during the first day of trading since the tariffs were announced.