Canadian oil and gas shares tumbled and the country's main stock index hit a one-month low on Wednesday, after the leftwing New Democratic Party surged to power in the oil-rich province of Alberta on promises that included energy industry reforms.

"Even now our inboxes are filling with messages expressing something between disbelief and dismay," analyst Andrew Bradford of Raymond James brokerage said after the party won an election on Tuesday to end 44 years of Conservative rule.

New Democrat Premier-elect Rachel Notley offered conciliatory words after her party swept to crushing victory, capitalizing on anger over the impact of the drop in oil prices on government programs.