Huge explosions at a warehouse for dangerous materials in the northeastern Chinese port of Tianjin killed at least 50 people, including 17 firefighters, and injured hundreds of others. The massive blasts late on Wednesday night sent fireballs into the air forming a mushroom cloud in the sky. More than 700 people are receiving treatment in hospital, the state-run news agency Xinhua reported. Seventy-one of them are said to be in a critical condition. READ MORE: ‘Is this a nuclear bomb?’: apocalyptic scenes in Tianjin, China, after industrial explosions The explosions late on Wednesday blew doors off buildings in the area and shattered windows up to several kilometers away. Twelve firefighters were killed tackling the blaze, Xinhua said. Thirty-six are missing, according to an earlier report from The Beijing News. Watch: Huge explosions rock Tianjin in northeast China The authorities suspended firefighting efforts at the warehouse on Thursday morning for a few hours due to a lack of clarity about what dangerous goods were inside and how much was stored. Firefighters returned later in the day and fires were still ablaze in four areas of the site, Xinhua reported. Roads were still blocked by debris around the warehouse, hampering efforts to put out the fires, the report said. Firefighters at the scene told the Beijing Times it might be possible to bring the fires under control before it got dark on Thursday evening. About 8,000 troops trained in anti-chemical warfare and about 1,500 armed police joined relief and rescue efforts on Thursday afternoon. Experts in biological and nuclear hazards have also joined the rescue effort, state media said. The city’s fire brigade said its personnel were sent to the warehouse at about 10.50pm on Wednesday night, 40 minutes before the first large explosion occurred. About 1,000 firefighters were deployed before teams were briefly pulled out on Thursday morning. Tianjin resident Zhang Siyu, whose home is several kilometers from the blast site, said she thought the explosions last night were an earthquake. “Only once I was outside did I realise it was an explosion. There was the huge fireball in the sky with thick clouds. Everybody could see it.” Zhang said she could see wounded people weeping. She said she did not see anyone who had been killed, but “I could feel death". A 28-year-old man told the South China Morning Post that he was driving on a bridge about 1km from the warehouse when the first explosion occurred. "The first blast was like setting off fire crackers and we were watching it from the car, but when the second one happened the shock wave was much stronger. "It was like shooting stars. There were also balls of metal falling from from the sky. We had to leave our car and escape at once leaving all of our personal belongs behind," the driver said. The force of the blast was so strong it buckled metalwork on the car and blew out all of its windows, he added.. Police in Tianjin said an initial blast took place at shipping containers in a warehouse for hazardous materials owned by Ruihai Logistics, a company that says it’s properly approved to handle hazardous materials. State media said senior management of the company had been detained by authorities. It is part of an industrial park, with some apartment buildings nearby. Among the chemicals the company handles are sodium cyanide, often used in the mining industry to help extract gold; plus toluene diisocyanate, a toxic organic compound, the China Youth Daily reported, citing the firm's website. The state-run Xinhua news agency said an initial explosion triggered other blasts at nearby businesses. The National Earthquake Bureau reported two major blasts before midnight, the first with an equivalent of 3 tonnes of TNT and the second with the equivalent of 21 tonnes. China’s President Xi Jinping has told the city authorities to contain the fire and rescue the injured, the China News Service reported. He also ordered them to fully investigate the cause of the explosions and hold people accountable if they were found to be responsible for the disaster, the report said. Photos taken by bystanders and circulating on microblogs show a gigantic fireball high in the sky, with a mushroom-cloud. Other photos on state media outlets showed a sea of fire that painted the night sky bright orange, with tall plumes of smoke. About 2 km from the explosion site is the luxury Fifth Avenue apartment complex on a road strewn with broken glass and pieces of charred metal thrown from explosion. Like surrounding buildings, the Mediterranean style complex had all its windows blown out and some its surfaces were scorched. “It’s lucky no one had moved in,” said a worker on the site, Liu Junwei, 29. “But for us it’s a total loss. Two years hard work down the drain.” “It had been all quiet, then the sky just lit up brighter than day and it looked like a fireworks show,” said another worker on the site who gave just his surname, Li. In one neighborhood about 10 to 20 km from the blast site, some residents were sleeping on the street wearing gas masks, although there was no perceptible problem with the air apart from massive clouds of smoke seen in the distance. “It was like what we were told a nuclear bomb would be like,” said truck driver Zhao Zhencheng, who spent the night in the cab of his truck. “I’ve never even thought I’d see such a thing. It was terrifying but also beautiful.” At the nearby Taida Hospital as dawn broke, military medical tents were set up. Photos circulating online showed patients in bandages and with cuts. One woman spent the night on the street after she was blown from her bed by shock waves from the explosions. "Even the elevator doors in our block were buckled," she said. Ruihai Logistics says on its website that it was established in 2011 and is an approved company for handling hazardous materials. It says it handles 1 million tonnes of cargo annually. Tianjin, with a population of about 15 million, is about 120 km east of Beijing on the Bohai Sea and is one of the country’s major ports. It is also one of China’s more modern cities and is connected to the capital by a high-speed rail line. Watch: Tianjin explosion large enough to be captured by Japanese weather satellite