The TSX composite index was off 330 points to 14,141 nearing midday. That was about the same as the index's decline for the previous week as a whole.
Basically everything was lower, as banks, tech stocks and industrials joined commodities in sliding into the red. (The only exception was health care, which eked out a 0.7 per cent gain on the day.)
The TSX is now at its lowest point since the middle of October, and Canada's benchmark stock index is now only up by a little over four per cent since the start of the year.
"The psychology is extremely negative. We’re back into panic mode,” said David Cockfield, managing director and portfolio manager at Northland Wealth Management. “The market in Canada is becoming more and more irrational."
"People are selling because the market is down and they think it’s going to go down further,” he said. “They’re probably going to be right because they’re selling."
Cockfield, who is waiting on the sidelines until the dust settles, said the oil and gas selloff has unnerved the market and now "investors are selling everything."
Bleak Chinese data prompts worries
One of the big catalysts was disappointing data out of China showing the country is buying less goods from overseas — and shipping out less to the rest of the world.
China's imports shrank unexpectedly in November, falling 6.7 per cent, while export growth slowed, fuelling concerns the world's second-largest economy could be facing a sharp slowdown.
China's crude oil imports rose nine per cent in November from October to 6.18 million barrels per day, suggesting the country may be boosting its reserves.
"If one looks at the overall economic indicators, they are all showing a picture of China which is stagnating rather than having strong growth," said Olivier Jakob, oil analyst at Petromatrix in Zug, Switzerland.- ANALYSIS: The winners and losers of cheap oil
That's bad news for a country like Canada, which has long been criticized for being heavily dependent on shipping natural resources to the rest of the world.
Oil prices keep sliding lower, with Brent Crude for January down $2.22 at $66.85 a barrel by 12:10 GMT, having fallen $2.30 to $66.77 US — its lowest since October 2009.
Oil was selling at $105 a barrel as recently as July, but the price has been falling ever since.
U.S. crude was down $1.60 at $64.24 a barrel, after hitting a session low of $64.14. The U.S. contract, also known as West Texas Intermediate, touched $63.72 last week, its lowest since July 2009.
In a report dated Dec. 5, U.S. investment bank Morgan Stanley said oil prices could fall as low as $43 a barrel next year.
"Without OPEC intervention, markets risk becoming unbalanced, with peak oversupply likely in the second quarter of 2015," Morgan Stanley analyst Adam Longson said.
"Given continued oversupply and still no sign yet that U.S. oil production starts to show any reaction, perhaps prices will continue to head lower," said Carsten Fritsch, senior oil and commodities analyst at Commerzbank in Frankfurt.