The Toronto Stock Exchange had its biggest loss of the year as North American markets plunged amid concerns that turmoil in Washington could hinder U.S. President Donald Trump's pro-business agenda.

The S&P/TSX composite index was down 269.65 points at 15,273.68 at the close, pulling back 1.73 per cent in a broad-based decline.

Eleven of the 12 subgroups closed lower, led by health care at 68.94 points, down 2.07 points, or 2.92 per cent.

Gold was the only advancer, adding 2.65 points, or 1.24 per cent, to 216.72 points.

The June gold contract rose $22.30 US to settle at $1,258.70 US an ounce on the New York Mercantile Exchange. Gold is often considered a safe haven in times of political uncertainty.

Volatile season

After a run-up that lasted six months, the market has been looking "really exhausted" with the Dow Jones industrial average and the S&P 500 levelling off since early March, Colin Cieszynski, chief market strategist at CMC Markets, told CBC News' Meegan Read.

"It's been a question for quite a while as to what it would take to finally push it over the edge and spark a correction. We often get corrections in the stock market between the middle of May and the middle of October. It's a seasonally much more volatile and weaker time of the year," he said.

"All of this turmoil around President Trump is arriving right at a time when the stock market is already vulnerable," said Cieszynski.

On Wall Street, stocks had their worst day since September of last year.

The Standard & Poor's 500 dropped 43.64 points, or 1.8 per cent, to 2,357.03. The Dow Jones industrial average lost 372.82points, or 1.8 per cent, to 20,606.93. The Nasdaq fell 158.63 points, or 2.6 per cent, to 6,011.24, a day after its latest record high.

The Canadian dollar hit 73.45 cents US, weaker than Tuesday's average price of 73.55 cents US. The U.S. dollar was at $1.3614 Cdn, up 0.18 of a cent.

Elsewhere in commodities, the June crude oil contract rose 41 cents to close at $49.07 US per barrel, the June natural gas contract fell 3.8 cents to about $3.19 US per mmBTU and the July copper contract shed 0.4 of a cent to roughly $2.55 US a pound.

Amid the turmoil surrounding the White House, investors are questioning Trump's ability to get his agenda through, said Quincy Krosby, market strategist at Prudential Financial..

"You could see gold was up, the dollar weakened and money went into the Treasury markets," Krosby said. "As long as it seems as if the Trump agenda can be realized before the midterm election, it's OK with the market, but once you introduce uncertainty into that trajectory, that's something the market has to reassess."