The Bangkok Metropolitan Administration (BMA) issued its most severe heat advisory on Thursday, with the heat index in Thailand's capital forecast to hit "extremely dangerous" levels for the first time this summer.

According to the BMA, the heat index is expected to reach or exceed 52 degrees Celsius on the day, prompting a warning to all residents to refrain from any outdoor activities, as exposure to these conditions poses a serious threat to public health.

The heat index calculates what the temperature "feels like" to the human body by combining air temperature and relative humidity. It is considered a critical indicator of heat risks, which range from exhaustion and dizziness to life-threatening heatstroke.

Health officials stressed that immediate medical attention should be sought if any abnormal symptoms occur, particularly among vulnerable groups such as young children, the elderly, pregnant women and individuals with underlying medical conditions or obesity.

The Thai Meteorological Department forecast maximum temperatures in the capital on Thursday to range between 34 and 38 degrees Celsius, with a 40% chance of thunderstorms in the greater Bangkok area.

To provide relief, the BMA has introduced "Heat Escape Rooms" at more than 300 designated cooling centers citywide.