Media playback is unsupported on your device Media caption An eyewitness captures the fear of those watching the explosions

Fires are still burning at the site of two massive explosions in the Chinese city of Tianjin, some 36 hours after the blasts.

Military chemical experts are testing for toxic gases and rescuers have been told to wear protective clothing.

At least 56 people died and more than 720 were injured, 25 critically and 33 seriously, in the explosions late on Wednesday evening, officials said.

But search teams did find one survivor in the debris early on Friday.

The man pulled from the rubble 32 hours after the blast was named as 19-year-old firefighter Zhou Ti, state-run news agency Xinhua reported.

Twenty-one firefighters are reported to be among the dead and several more are missing. Fire crews were already at the site when the explosions took place, having been called out after reports of a container fire.

Tianjin's fire department chief Zhou Tian told reporters that more than 1,000 firefighters and 140 fire engines were at the site on Friday.

The Tianjin Port Group Company said dozens of its employees remained unaccounted for, according to Xinhua.

Media playback is unsupported on your device Media caption Aerial views of the site of the explosion in Tianjin

The warehouse that exploded in the port area is owned by a company called Ruihai Logistics, which specialises in handling hazardous goods.

The company's website says these include compressed gas, flammable liquid and toxic chemicals - some of which become highly explosive when mixed with water.

But city officials said on Friday they still did not know what materials were at the warehouse at the time of the fire, or what caused the blasts.

Gao Huaiyou, deputy director of Tianjin's work safety watchdog, said there were discrepancies between accounts by company and customs officials, adding that damage to company offices made it hard to identify the chemicals.

Image copyright AFP Image caption Rows upon rows of new vehicles were destroyed by the explosions

Image copyright Reuters Image caption Rescue teams could be seen recovering a body from the blast site on Friday

The BBC's John Sudworth in Tianjin says that once the fire is extinguished, the chemical containers will be moved to a safety zone, away from the heat, so that the contents can be analysed.

Tianjin's residents remain nervous, he adds, with some posting concerns online about the environmental impact and suspicions that the public may not be hearing the full truth.

Media playback is unsupported on your device Media caption Dashboard camera captures China blast shockwave

The head of Tianjin's environmental protection bureau, Wen Wurui, said pollution levels were being monitored and other officials insisted any contaminants had been contained.

Fires are still sending plumes of smoke over the destroyed buildings, burned-out vehicles and crumpled shipping containers that bore the brunt of the explosions.

Tianjin explosions

What we know about explosions: Much of what happened is unclear, but here is what we do know

Fears after explosions: The questions being asked by Chinese citizens

Potent chemical mix behind blasts: What caused the dramatic explosions?

Tianjin in profile: More about Tianjin, one of the busiest ports in the world

'Seismic scale' of blasts: Explosions so large they registered on seismometers

Blast 'like end of the world': Residents' stories

Pictures reveal devastation: The latest images from Tianjin

'Netizens' critical of coverage silenced: Authorities remove social media posts

The People's Daily, the official newspaper of the Chinese Communist Party, said that emergency services were "trying to remove all the 700 tonnes of sodium cyanide" stored at the site.

The local fire chief said further recovery efforts would be slow because of the potentially complex mix of chemicals at the site.

"Many types of different materials with different characteristics are mixed together and could at any time result in a chemical reaction or explosion,'' Zhou Tian said.

One small explosion was reported at the site on Friday morning.

Image copyright AFP Image caption The initial fire was reported to have started in a container at the port

Image copyright Reuters Image caption Thousands of people have taken up temporary shelter at nearby schools

The People's Daily said the facility had "clearly violated" safety rules that say dangerous materials must be stored at least 1km (0.6 miles) away from public buildings and main roads.

State media said the manager of the Ruihai Logistics site had been detained.

Meanwhile, the government said nationwide safety inspections would be carried out on industrial sites in a bid to learn the "extremely profound" lessons from the tragedy.

Chinese Premier Li Keqiang has promised "open and transparent information disclosure" on the investigation.

The two explosions, seconds apart, caused a fireball visible from space and a shockwave that damaged buildings within a 2km radius (1.5 miles). The second of the blasts was the equivalent of 21 tonnes of TNT.

Officials said more than 6,000 residents forced to leave their homes had been relocated at several nearby schools that are being used as temporary shelters.