With the city experiencing the hottest day of the summer this year at temperatures of nearly 39 C Sunday, power authorities issued a warning to residents telling them to prepare for the possibility of a blackout.

Blocks of ice were placed at the Bund Sunday to help visitors stay cool in the extreme heat when temperatures reached nearly 39 C. [Global Times]

The Shanghai Municipal Electric Power Company issued the caution to residents in Pudong New Area as well as Yangpu and Baoshan districts, over fears that the city grid may overload as an increasing number of households consume more energy by using their air-conditioning units to keep cool.

The city plans to switch to the State-owned power generator during peak hours today, in an effort to alleviate pressures to the municipal network that has been brought on by rising temperatures in the city.

Meanwhile, Sunday's 38.2 C temperatures also marked the twelfth day of the year for city temperatures to surpass highs of 35 C, a threshold that weather experts consider as crucial for residents to take measures to prevent heatstroke.

The extreme heat is expected to last until Wednesday, with temperatures hovering between 37 C and 39 C, said authorities.

But the good news is that authorities are forecasting slightly cooler days starting from Thursday, when cool air from the East China Sea will help bring temperatures down a few degrees to as low as 34 C.