Chinese authorities are treating thousands of tonnes of polluted water at the Tianjin port, which was rocked by warehouse blasts last week.

Water in the crater and pipelines at the blast site will be processed and drained to make room for the coming rain, said Bao Jingling, chief engineer of Tianjin's bureau of environmental protection, on Tuesday morning.

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

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

A cofferdam at the site will be reinforced to prepare for rainstorms, Bao added. The dam was built around the 100,000-square-meter core area of the blasts to prevent the outflow of contaminated water during rainy weather.

Authorities are also closely monitoring the air quality as they fear rain water will set off chemical reactions with the scattered chemicals and release toxic gases into the air, Bao said.

A total of 114 people have been confirmed dead, and 70 remain missing after two huge explosions occurred before midnight on Aug. 12 at a warehouse for hazardous chemicals.

Officials said about 700 tonnes of sodium cyanide were at the blast site but remain mostly unaffected. .