Fires are still burning at the site of two massive explosions in the Chinese city of Tianjin, some 36 hours after the blasts. A team of military chemical experts is testing for toxic gases at the scene and rescuers have been ordered to wear protective clothing, state media said. At least 50 people died and more than 700 were injured, 71 critically, in the explosions on Wednesday evening. Meanwhile, search teams found a survivor in the debris on Friday. The survivor was named as 19-year-old firefighter Zhou Ti, state-run news agency Xinhua reported. Officials said earlier that 17 firefighters were among the dead and 18 others are said to be missing. Fire crews were already at the site when the explosions took place, having been called to 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 still battling flames at the scene on Friday. The Tianjin Port Group Company said dozens of its employees remained unaccounted for, Xinhua said. 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 goods 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 the cause of the blasts was. However, they said the site had been sealed off and, as far as they knew, any contaminants were contained in that location. Gao Huaiyou, deputy director of Tianjin's work safety watchdog, told reporters that there were major discrepancies between the accounts of company managers and customs officials. He said damage to the company's office also made it difficult to identify the chemicals.