Wall Street shares plunged on Monday as investors fled technology stocks amid resurgent trade war worries, with key indexes trading below their 200-day moving averages and the S&P 500 closing below that pivotal technical level for the first time since Britain's vote to leave the European Union in June 2016.

The first trading day of the second quarter began with a broad selloff concentrated in the technology and consumer discretionary sectors, as losses by Amazon.com (AMZN.O), Tesla (TSLA.O) and Microsoft (MSFT.O), among others, took center stage from retaliatory trade measures China unveiled on Sunday.

"ItRs more complicated than just a tech selloff. What's hurting everything is that the S&P went through its 200-day moving average," said Brian Battle, director of trading at Performance Trust Capital Partners in Chicago. "That attracts momentum sellers and they don't care what the fundamentals are."

The Dow Jones Industrial Average fell 458.92 points, or 1.9 per cent, to 23,644.19 after dipping below its 200-day moving average. The S&P 500 fell 58.99 points, or 2.23 per cent, to 2,581.88 and the Nasdaq Composite dropped 193.33 points, or 2.74 per cent, to 6,870.12.

Amazon.com was the biggest drag on the S&P 500, down 5.2 per cent, as President Donald Trump continued his twitter attacks on the online retailer.

All 11 major sectors of the S&P 500 closed lower, with the biggest losses seen by the consumer discretionary and technology indexes, which were down 2.8 per cent and 2.5 per cent, respectively.

The tech-heavy Nasdaq was dragged lower by Microsoft, Intel (INTC.O), Apple Inc (AAPL.O), Facebook (FB.O) and Alphabet (GOOGL.O).

Shares of Tesla Inc ended the day down 5.1 per cent after the company was reported to be making 2,000 Model 3s per week, missing its 2,500 target.

The electric automaker's losses extend last week's near 14-per cent decline as investigations of a fatal California crash and a Moody's credit downgrade weighed on the stock.

Health insurer Humana Inc's (HUM.N) shares closed up 4.4 per cent on news it was in talks with Walmart to expand their partnership or possibly be acquired by the retailer . Walmart (WMT.N) stock fell 3.8 per cent.

U.S. Treasury yields fell to two-month lows as investors fled sliding stocks for safety ahead of Friday's closely watched jobs report.

Declining issues outnumbered advancing ones on the NYSE by a 4.17-to-1 ratio; on Nasdaq, a 4.14-to-1 ratio favored decliners.

Volume on U.S. exchanges was 7.71 billion shares, compared to the 7.29 billion average over the last 20 trading days.

CANADIAN STOCKS

Canada's main stock index fell on Monday, led by energy and financial shares, as oil prices tumbled and investors worried about an escalating trade war between the United States and China.

The Toronto Stock Exchange's S&P/TSX composite index, which fell 5.2 per cent in the first quarter, closed down 153.84 points, or 1.0 per cent, at 15,213.45.

Losses for the index came as U.S. stocks plunged. Investors on Wall Street fled technology shares amid resurging trade worries.

China raised tariffs by up to 25 per cent on U.S. products, in response to U.S. duties on aluminum and steel imports.

Eight of the index's 10 main groups ended lower.

The energy group fell 2.2 per cent as crude oil prices slumped. U.S. crude oil futures settled nearly 3 per cent lower at US$63.01 a barrel.

Financials declined 0.9 per cent and information technology retreated 1.7 per cent.

The largest percentage gainer on the index was Transcontinental Inc (TCLa.TO), which rose 9.7 per cent, while the largest decliner was Prometic Life Sciences Inc (PLI.TO), down 15.9 per cent.

Gold futures benefited from demand for safe haven assets, rising 1.3 per cent to US$1,340.2 an ounce.

The materials group, which includes precious and base metals miners and fertilizer companies, added 0.1 per cent.

The TSX posted four new 52-week highs and 10 new lows.