Thousands of dead fishes washed ashore a lake near the blasts site in Tianjin on Thursday, raising fears that poisonous chemicals released from the affected warehouse might have made its way into the waters.

On Thursday afternoon, fishermen saw "heaps of dead fish" washing up on the shore at a lake in Tianjin located 6 km from the deadly blasts site, according to Chinese daily Shanghaiist.

The incident alarmed the local residents, who told local media that they have never seen anything like it before.

Tianjin officials are currently investigating the "mysterious death of the fish in the Tianjin lake". The Tianjin Environmental Bureau (TEB), however, has maintained that air and drinking water in the city were safe and "water contamination has been contained effectively".

TEB head Deng Xiaowen told the media on Thursday there could be several reasons for the "dead fish" washing up on the shore.

He said that the offshore area close to the blasts zone, inside the Haihe River Dam, has been subject to regular monitoring, and cyanide was not detected in the water body, China Daily reported.

The development comes just a day after some reports claimed that the waters around the site of the deadly chemical blasts in Tianjin port city has cyanide levels as high as 356 times beyond the safety levels.

On Tuesday, following the first chemical rains that hit Tianjin after the deadly blasts covered the city streets with white foam and local residents who came in contact with the rainwater complained of "stinging sensation" and rashes.