TIANJIN, Aug. 18 -- Thousands of tonnes of contaminated water at Tianjin Port, the site of two massive warehouse explosions last week, needs to be treated, over fears that rain may exacerbate the problem.

Pipeline and ground water at the blast site will be processed and drained to make room for the coming rain, said Bao Jingling, chief engineer of Tianjin bureau of environmental protection, on Tuesday morning.

The environmental official estimates the volume of contaminated water in the crater left by the blasts as "tens of thousands of tonnes."

On Monday, water tested at eight of the 40 water monitoring stations in the area were found to contain excessive cyanide, with some samples containing 28.4 times more than the standard, according to Bao.

Bao made the remarks as the northern city witnessed a light-rain shower on Tuesday morning, stoking fears that rescue efforts would be disturbed and contamination would spread at the site where hundreds of tonnes of toxic cyanide were stored.

A cofferdam will be reinforced to prepare for rainstorms, he said. The dam was built around the 100,000-square-meter core area of the blasts to prevent the outflow of contaminated water should it rain.

Air quality is also being closely monitored over fears that rain might set off chemical reactions with the scattered chemicals and release toxic gases, he added.

The environmental authority may establish more monitoring stations, Bao said, adding that monitoring personnel from other cities and provinces have been despatched to Tianjin.

A total of 114 people have been confirmed dead, and 57 remain missing after two huge explosions just before midnight on Aug. 12 at a warehouse that held hazardous chemicals.

Officials say that around 700 tonnes of sodium cyanide stored at the blast site remains mostly unaffected.

According to He Shushan, vice mayor of Tianjin, as of Monday night chemical specialists had searched a radius of three kilometers around the blast site's core area. "We have cleaned 150 to 160 tonnes of sodium cyanide."