Drone footage of the aftermath of explosions in Chinese city of Tianjin.

A 19-year-old Chinese fireman has been pulled alive from the smouldering rubble of the Tianjin explosion, more than 36 hours after the detonation caused two fireballs so large that they were visible from space.

Fireman were still battling to control the fires after the warehouse blast, which was the equivalent of 24 tons of TNT exploding, and which killed at least 56 people, injured 720 and devastating the port in the country's north east.

At least 21 firemen were among the victims of the explosions - making it possibly the highest number of fatalities among fire crews since the founding of the People's Republic of China in 1949.

AP Chinese firefighter Zhou Ti is treated in Taida Hospital in Tianjin.

The high death toll made the survival of Zhou Ti all the more remarkable.

Zhou was being treated for chest injuries at a hospital in Tianjin and was in stable condition, the city government said. Images showed the teenager lying on a hospital bed, his eyes closed, wounds covering most of his face and a net bandage on his head.

1 of 13 JASON LEE / REUTERS A bulldozer works near the site of the explosions at the Binhai new district, Tianjin. 2 of 13 CHINA DAILY/REUTERS An injured woman receives treatment at a hospital. 3 of 13 CHINA STRINGER NETWORK/REUTERS Damaged vehicles are seen as smoke rises from shipping containers. 4 of 13 CHINA DAILY/REUTERS Firefighters work at the site as smoke rises from the debris after the explosions at the Binhai new district in Tianjin, China, August 13, 2015. 5 of 13 JASON LEE/REUTERS Smoke rise from container boxes near the site of the explosions at the Binhai new district, Tianjin. 6 of 13 JASON LEE/REUTERS Damaged buildings and cars are seen near the site of the explosions at the Binhai new district, Tianjin. 7 of 13 REUTERS Smoke rises over the site of the explosions at the Binhai new district in Tianji. 8 of 13 REUTERS/STRINGER/CHINA Makeshift shelters have popped up around the area of the blast. 9 of 13 REUTERS A man checks his mobile phone near overturned shipping containers after the explosions. 10 of 13 REUTERS Shipping containers damaged by the explosions. 11 of 13 REUTERS Damaged vehicles are seen under bridges close to the site of the explosions. 12 of 13 STRINGER/CHINA/REUTERS Vehicles are seen burning after blasts in Tianjin municipality. 13 of 13 REUTERS A damaged vehicle is seen near the site of the blasts at Binhai new district in Tianjin municipality.

READ MORE: Gigantic Tianjin blasts leave wasteland

* Moment of explosion caught on CCTV

VIDEO: Massive Tianjin explosion 'like a nuclear explosion'

YouTube A huge explosion has hit the Chinese city of Tianjin, injuring dozens of people.

Some of the chemicals known to have been stored in the warehouse explode on contact with water, raising questions over whether the firefighters who attended the intial fire prior to the explosions had followed due protocol.

"The firefighters were at the centre of the explosion and were unprepared," said Zhou Tian, the head of the Tianjin firefighting bureau.

Authorities in the city of Tianjin have so far been unable to identify the cause of the blast, but said they had concerns over the security of hazardous chemicals stored within the disaster zone.

The warehouse, designed to house dangerous and toxic chemicals, was storing mainly ammonium nitrate, potassium nitrate and calcium carbide, according to police.

The People's Daily, the Communist Party mouthpiece, said that the facility "clearly violated" safety regulations. Six senior executives from Ruihai, the company that managed the warehouse, have been detained.

Meanwhile fears over public health and safety were raised after chemical experts found sodium cyanide in sewers near the blast zone.

At least 700 tons of sodium cyanide were stored at the site according to an initial report by Beijing News, published on Thursday. On Friday, however, the post had been removed from the news website - and Chinese authorities have attempted to control the spread of information about the blasts on social media and in the press.

"It is likely that the cyanide, which is poisonous, will evaporate because of the warm temperature in Tianjin," said a safety management specialist in Beijing, who spoke to The Daily Telegraph on the condition of anonymity.

"Residents nearby should be evacuated and protection measures should be taken. If cyanide in the air is inhaled it will cause coughing and pharyngitis."

Authorities said they were "closely monitoring" the water and air around the blast zone, while drains leading from the blast area into the Bohai Sea were closed.

But not all residents were reassured. "I'm really scared, but I don't even know what to be scared of. The government hasn't said anything," said Liu Zongguang, 50.