Canada's deadly heatwave, the most severe on record, is moderating slightly, but still looks this week to erase high temperature marks set decades ago, a government climatologist said on Wednesday.

At least 233 people died in the Pacific coast province of British Columbia between Friday and Monday, about 100 more than the average for a four-day period, the BC Coroners Service said.

The heatwave has scorched crops across the Prairies, where farmers grow much of the world's wheat and canola, driven up natural gas prices in the fourth-largest global producer, and increased the risks of wildfires.