Japan's biggest electric utilities are firing up old fossil fuel power plants and ramping up others that are already operating, pushing to meet demand as power prices hit record highs amid a deadly heat wave.

The deployment of older, dirtier stations that use commodities such as crude and fuel oil highlights the lingering effects of the Fukushima nuclear disaster in 2011, which has left most of the country's reactors offline as operators upgrade them.

Like many other regions of the world, Japan has been hit by record temperatures in a two-week heat wave, with more than 80 people dying and thousands rushed to emergency rooms.