TIANJIN, China — Chinese leaders scrambled on Thursday to contain the fallout from an apocalyptic fire in this major port city that appeared to reflect an enormous regulatory failure, caused by a witch’s brew of toxic chemicals housed within a mile of thickly populated areas.

President Xi Jinping personally ordered subordinates to ensure that all unaccounted-for victims were found after the Wednesday night disaster, and the army sent more than 200 hazardous-chemical specialists in protective suits to investigate.

But the authorities also sought to constrict the flow of information as many traumatized citizens seethed over how such a disaster could happen and expressed frustration over what they called a lack of reliable guidance before or after the fire.

They wondered if even the air was safe because of the smoke, still billowing hours later from vestiges of the inferno, which destroyed an industrial zone near the port. Many people wore masks.