'Firefighter' pulled from Tianjin blast wreckage

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A survivor has been pulled out from the wreckage left by the huge explosions in Tianjin, China, more than a day after the deadly blast, according to media reports.

Details on the rescue are scarce and it is not clear if the man had been trapped since Wednesday night under the rubble of the hazardous goods warehouse at the center of the explosions. State media outlet Xinhua reported that the survivor was a 19-year-old firefighter.

According to Reuters at least 54 people, including a dozen firefighters, were killed and more than 700 people injured in two blasts - a small first explosion followed by a second one equivalent to 21 tons of TNT exploding - that shot massive fireballs into the sky and wreaked havoc on the port-side warehouse district of the northern city.

Read MoreChina experts focus on chemicals in Tianjin explosion

Investigators are continuing to search for clues as to precisely what caused the explosions at the warehouse, which is designed to house toxic chemicals and gas. Citing police reports, Reuters said that the warehouse mainly stored ammonium nitrate, potassium nitrate and calcium carbide at the time of the blasts.

Chemical experts suspect that an explosion could have been caused if firefighters, who had been called to attend a fire in the area shortly before the blast, sprayed the calcium carbide with water. Calcium carbide reacts with water to create acetylene, a highly explosive gas, they said.

Hazardous materials

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Concerns that the blast has spread hazardous substances into surrounding areas have intensified after the Ministry of Environmental Protection revealed that pollutants including chemical oxygen demand (COD) and cyanide were found three times and eight times higher than the usual levels in two drainage outlets near the blast site.

This caused some panic on Chinese social media, with users begging for "the truth". One user called Me and 7 Dogs wrote: "stop lying to us ppl."

Tianjin is home to around 15 million people, making it one of the biggest cities in China. It is also the site of one of China's biggest ports. More than 200 military specialists in handling nuclear and biochemical materials have been deployed at the site to assist with the investigation.

-CNBC's Haze Fan and Reuters contributed to this report.