Record-breaking heat prolongs misery for millions across US

The sky glows orange as the sun rises near the US Capitol, Washington Monument and Lincoln Memorial in Washington (Alex Brandon/AP)

A relentless heatwave continued to bake most of the United States on Friday, with numerous areas expected to see record-breaking temperatures and forecasters warning there would likely be little relief throughout the weekend for most areas.

The steamiest conditions on Friday were expected in parts of Ohio and Indiana, where heat indexes were likely to soar past 37.8C and remain there most of the day.