Environmental authorities near the blast site in Tianjin asked the public to be aware of rain, as the first precipitation since last week's deadly explosion hit the port city on Tuesday morning.

Bao Jingling, chief engineer of the municipal Bureau of Environmental Protection, said the best way to cope with rain was to keep away of it.

Torrential rain hit the scene in Tianjin’s Binhai New Area, prompting fears that water could be polluted by toxic chemicals remaining at the site and contaminate surrounding areas and affect public health.

Bao said toxic chemicals could evaporate in rain and may cause indirect pollution, but no direct damage would be caused as long as there were no further blasts.

The explosions in Tianjin last week killed at least 114 and 57 others remain missing as of 11 am on Tuesday.

Bao said sodium cyanide, a highly toxic chemical compound that can affect the body's ability to use oxygen, can evaporate after being dissolved in rain and spread into surrounding areas.

At least 700 metric tons of sodium cyanide has been found on the blast site and authorities said hydrogen peroxide will be used to break down toxins into less poisonous chemicals.

Bao said rain will also take some of the harmful chemicals into the drainage system and the government has blocked access to the sea and rivers to prevent further contamination.

"We will keep a close eye on the environmental index. Once any irregular data is found, emergency measures will be conducted," he said.

Experts said people may feel choking after inhaling a minor amount of oxygen being contaminated by sodium cyanide gas, according to a report carried by Caijing.com, a financial news portal.

Previously, photos depicting Premier Li Keqiang and other officials visiting the blast site on Sunday showed them not wearing masks or taking any other precautions in a gesture to demonstrate the leadership's confidence in local air quality, experts said.