China explosions: Teenage firefighter pulled from wreckage after 32 hours as authorities warn another blast could hit Tianjin 'at any time'

Experts are investigating the cause of the disaster in the Chinese city

A teenager who survived for 32 hours beneath the rubble of devastating explosions in Tianjin has been rescued - as authorities warned another blast could happen “at any time”.

Zhou Ti, a 19-year-old firefighter, was pulled from the disaster zone at dawn and taken to hospital, where he was being treated for face, chest and foot injuries, according to Chinese state broadcaster CCTV.

The rising death toll includes 17 firefighters who were sent in to tackle a blaze that preceded a series of chemical blasts in shipping containers on Wednesday.

Two huge explosions, including one with the force of 21 tons of TNT, came just 30 seconds apart. They were so large they could be seen from space and were registered by earthquake sensors.

Warning: This footage contains extremely strong language

Footage taken from a nearby high-rise building showed the initial explosion before the second blast blanked out the screen with white light, fading to show fireballs shooting into the air from a flaming mushroom cloud.

The blasts torched cars and reduced buildings to blackened shells, starting fires that are still burning among hazardous materials, prompting fears of further blasts.

“Forces from all sides are searching for the (remaining) missing firefighters,” said Zhou Tian, the head of Tianjin Fire Department.

“Many types of different materials with different characteristics are mixed together and could at any time result in a chemical reaction or explosion.”

At least 50 people were killed and 700 injured and the search for survivors continues. Authorities said the toll could have been much higher if the disaster hit a more populated area.

The containers that exploded belonged to Ruihai International Logistics, a firm handling chemicals ranging from flammable gases and liquids like compressed natural gas and ethyl acetate, to toxic chemicals including sodium cyanide and toluene diisocyanate.

The warehouse where they were being held was designed to house dangerous and toxic chemicals and had been storing mainly ammonium nitrate, potassium nitrate and calcium carbide at the time of the blasts, according to police.

Gao Huiyou, deputy director of occupational safety in Tianjin, said records inside the building were destroyed in the disaster and extinguishing the continuing fire was difficult before of the complex mix of chemicals still present.

The explosions at a warehouse in the port city of Tianjin were so huge they were picked up as a bright white spot by the Japan Meteorological Agency’s satellites (AFP/Getty)

Chemical safety experts have said that calcium carbide reacts with water to create acetylene, a highly volatile gas that could explode if sprayed by firefighters’ hoses.

Lei Jinde, the deputy propaganda department head of China's fire department, a part of the Ministry of Public Security, told ThePaper.cn that the first group of fire fighters on the scene had used water.

“We knew there was calcium carbide inside but we didn't know whether it had already exploded,” he said.

“At that point no one knew, it wasn't that the fire fighters were stupid.”

Concerns have also been raised in Chinese media about possible violations of packaging standards identified by safety inspectors two years ago.

The aftermath of the massive explosions at a warehouse storing toxic chemicals in Tianjin (EPA)

President Xi Jinping said those responsible should be "severely handled".

David Leggett, a chemical safety expert based in California, told Reuters the acetylene explosion could have detonated the ammonium nitrate, explaining the second and larger explosion.

Thousands of residents have been moved into nearby schools after their apartment buildings and homes were damaged by shockwaves from the explosions.

Meanwhile, some of the world’s largest corporations are counting the cost of damage to their stock at the port.

Windows were blown out of apartment buildings near the site of the explosions (AFP/Getty Images)

Toyota Motor Corp said windows were broken at its passenger vehicle assembly plant but no one was hurt, while Renault said more than 1,000 of its cars were damaged but no staff were hurt.

Mining giant BHP Billiton said its port operations and shipments were disrupted but its iron ore discharging berth had not been damaged.

John Deere & Co, the American farm and construction equipment company, said several workers in their homes at the time were injured, some critically.

A team from the International Atomic Energy Agency's Beijing environmental emergency response centre and 214 Chinese military nuclear and biochemical materials specialists have travelled to Tianjin as investigations continue.

Additional reporting by PA and Reuters