Southern US braces for near record-breaking heatwave

Phoenix, Arizona, in middle of historic stretch of sweltering temperatures

Residents cool off at Barton Creek Pool in Austin, Texas. AFP

A vast corridor across the southern US, stretching from California to Florida, is facing a lengthy blast of excessive heat, with stifling conditions forecast for this week.

An excessive heat warning is set to remain in effect until next weekend in Phoenix, Arizona, as the US south-west continues to swelter.

Phoenix is in the midst of a near record-breaking heatwave after recording temperatures of greater than 43°C for 10 days in a row. The National Weather Service estimates the south-western US city has a 50 per cent chance of breaking the record of 18 days in a row, which was set in 1974.

Hotter temperatures are still to come.

Forecasters expect Phoenix to record high temperatures between 41°C and 44°C this week, with the most oppressive heat arriving in the middle of the week.

Weather officials are also forecasting a prolonged period of heat in southern California, which will stretch into next weekend.

The inland is expected to bear the brunt of the heat with highs, reaching between 33 and 38°C on Monday and 38 to 44°C for the rest of the week. Southern California's coast is forecast to receive much cooler weather, the NWS agency in Los Angeles said.

The NWS said heat becomes more dangerous if it lasts for more than one day.

Residents within the heat-drenched areas were advised to stay indoors in air-conditioned places. People are also advised to wear light and loose fitting clothing, and to keep hydrated.

That heat will also stretch into Texas, whose energy grid has been tested by the conditions.

Del Rio, a town near the US southern border, has already set 12 daily temperature records.

Austin, the state capital, is forecast to record daily temperatures of 39°C this week. Dallas and Houston are expected to face stifling conditions as well.

Sweltering conditions in Florida are expected to last throughout this week as well.

The NWS issued a heat advisory for all of south Florida until Wednesday evening after the region's heat index ranged from 40 to 42.7°C. A heat index over 39 is considered to be dangerous.