Rains are likely to complicate rescue efforts and may spread pollution at China's Tianjin port, which was rocked by explosions at a warehouse last week that left 114 people dead.
China's central meteorological authority has forecast a thunderstorm over the blasts site, where hundreds of tonnes of toxic cyanide still reside, reported Xinhua news agency.
A chemical weapon specialist at the site told Xinhua that rain water may merge with the scattered chemicals, adding to the probability for new explosions and spreading toxins.
Authorities have said the cofferdams built around the 100,000-square-meter core area of the blasts will receive constant reinforcement to prevent the outflow of contaminated water after it rains.
Seventy people are still missing after two huge explosions occurred before midnight on Aug 12 at the warehouse that stored hazardous chemicals.
Officials said about 700 tonnes of sodium cyanide were at the blasts site but remained mostly unaffected.
