TORONTO -- North American stock markets slipped slightly lower Thursday as metals took a hit amid trade uncertainty and the U.S. and China imposed tariffs on each other's goods.

Markets have been volatile but have traded in the summer on headlines, said Ian Riach, CIO of Fiduciary Trust Canada.

"So I think a lot of the trade talk around the U.S. and China today...probably has a broad effect on the North American markets," he said in an interview.

The world's two largest economies imposed 25 per cent tariffs on $16 billion of each other's goods, including automobiles and factory equipment. The previously announced increases come as envoys met for their first high-level talks in two months.

Canada's main stock index edged lower, led by losses in the materials sector, base metals and gold weighed on the market.

The S&P/TSX composite index was down 20.55 points at 16,326.79 Thursday, after reaching an intraday high of 16,358.58 on 171 million shares traded.

The materials sector was down 1.5 per cent as almost all companies closed down on the day, led by Tahoe Resources and New Gold, on a stronger U.S. dollar.

The Canadian dollar traded down at 76.55 cents US compared with an average of 76.83 cents US on Wednesday.

Health care gained 1.45 per cent led by cannabis companies Canopy Growth Corp. and Aphria Inc.

Information technology, industrials, energy and telecom services were up by less than a percentage point. Financials, utilities, consumer staples, real estate and consumer discretionary were down slightly.

In New York, the Dow Jones industrial average was down 76.62 points at 25,656.98. The S&P 500 index was down 4.84 points at 2,856.98, while the Nasdaq composite was off 10.64 points at 7,878.46.

U.S. markets face a lot of uncertainty right now as trade issues gain lots of public attention while interest rates and earnings are longer-term drivers of activity, said Riach.

"In the short-term there's a lot of uncertainty particularly around trade and just the political situation in the U.S. that I think has investors just a little bit nervous," he said.

"Here in Canada obviously with the U.S. being the largest importer of our goods, any trade uncertainty there I think just tends to put a ceiling on stock prices."

The October crude contract was down three cents at US$67.83 per barrel and the September natural gas contract was up 0.8 of a cent at US$2.964 per mmBTU.

The December gold contract was down US$9.30 at US$1,194.00 an ounce and the September copper contract was down 1.9 cents at US$2.654 a pound.