San Francisco, Jun 28 (IANS): The US National Weather Service (NWS) has announced that the first heat wave of the summer is expected to hit Southern California later this week.

With a high-pressure system building over Southern California, temperatures are forecast to heat up Thursday and into the weekend, culminating in a heat wave over the Fourth of July holiday, Xinhua news agency quoted the NWS as saying in its latest update.

"First heat wave of the summer is expected by the holiday weekend, focused across interior areas. Triple digit temperatures likely across the hottest interior areas," the weather service added.

Health officials are urging residents to avoid heat stress by seeking out shade or air-conditioned locations, drinking more water and avoiding sunburn.

The announcement comes amid an extreme heat wave that has baked much of the southern US , with over 55 million people currently under heat alerts.

The heat wave has scorched Texas, Oklahoma, New Mexico, among other southern parts over the past week, setting or challenging all-time records.

The life-threatening "oppressive" heat dome was producing "dangerous heat and humidity in Texas and spread into the lower Mississippi River Valley", according to the NWS.

Extreme heat has been the greatest weather-related cause of death in the US for the past 30 years -- more than hurricanes, tornadoes, flooding or extreme cold -- killing over 700 people per year, according to the US National Oceanic and Atmospheric Administration.

In addition, the heat crisis does not affect people equally. Extreme heat mortality disproportionately affects Native American and Black communities, as well as those living in the urban core or very rural neighbourhoods, according to the US Centers for Disease Control and Prevention.

Studies have shown that climate change is making heat waves both more frequent and more intense, increasing the risks of heat-related illnesses and deaths, droughts and wildfires.