Authorities in China said a river running near the Tianjin chemical explosion site was not contaminated with cyanide after a massive amount of dead fish appeared in the local waterway.

The Tianjin Environmental Monitoring Centre tested water samples from a section of Haihe River, where thousands of dead fish surfaced on Thursday, eight days after chemical blasts ripped apart a logistics centre nearby.

Dead fish in Haihe River in Tianjin. Photo: Beijing News.

Pictures posted on Chinese social media by residents showed the white fish accumulating along the river bank, drawing curious residents to the scene.

Dead fish in Haihe River in Tianjin. Photo: Beijing News.

Deng Xiaowen, director of the Tianjin Environmental Monitoring Centre, said at a press conference on Thursday that “there could be many reasons” for the phenomenon. Deng said dead fish in Haihe River is not uncommon as it has happened in the past during hot weather.

Dead fish in Haihe River in Tianjin. Photo: Beijing News.

Hours later, the Centre released results of its water tests. The level of cyanide in the samples was shown as “zero.”

Authorities take water samples from Haihe River. Photo: Weibo.

Cyanide is a rapidly acting and potentially lethal chemical, according to the US Centers for Disease Control and Prevention. Authorities earlier confirmed 700 tonnes of the highly poisonous sodium cyanide were stored on the site of the explosions.

Residents took to social media to express their doubt over the test results. One user on China’s microblogging site Weibo said: “Hot weather? How about drowning?” Actor Sun Haiying joked: “I heard from netizens that the dead fish were illegal immigrants from North Korea.”

Meanwhile, cyanide level in water samples taken from a massive crater created by the force of the explosions exceeded safety limit by over 800 times.