KARACHI, Pakistan — Heat waves have become common this time of year in Karachi, Pakistan’s sprawling seaside port city. Still, the latest one caught its 20 million residents off guard.

It was all anyone here could talk about last week as people moved lethargically about their days, helpless to avoid temperatures that sometimes soared to above 110 degrees Fahrenheit, leaving people in a fever-like haze, even in the shade.

The heat, radiating from roads and cement buildings well into the night, was made worse by the city’s notorious lack of green space. Shops and households that can afford air-conditioners cranked them up, but most people were left with few options: wet washcloths and electric fans, and those only for the few hours when the power was on.

The streets, normally congested with traffic, became eerily empty around noon. The traffic police listlessly motioned at cars from under umbrellas as people made their way indoors or hid for a few moments in the shadow of one of the city’s many concrete towers — anywhere that could provide some respite.