TIANJIN, China » The death toll from the fiery explosions at a warehouse of hazardous chemicals climbed Thursday to 50, and the Chinese government sent experts to the shattered and smoldering port to assess any environmental dangers from the spectacular blasts.

More than 700 people were injured and dozens were reported missing in the explosions shortly before midnight Wednesday that demolished a workers’ dormitory, tossed shipping containers as if they were toy blocks and turned a fleet of 1,000 new cars into scorched metal husks. Windows were shattered for miles around by the shockwaves.

There was no indication of what caused the disaster in one of China’s busiest ports, and authorities tried to keep a tight rein over information by keeping reporters well away from the site. Social media users complained their posts about it were deleted.

More than 1,000 firefighters were sent to the mostly industrial zone in Tianjin, a petrochemical processing hub about 75 miles east of Beijing.

Tianjin is the 10th largest port in the world by container volume, according to the World Shipping Council, and the seventh-biggest in China. It handles vast amounts of metal ore, coal, steel, cars and crude oil.

Ships carrying oil and "hazardous products" were barred from the port Thursday, the Tianjin Maritime Safety Administration said on its official microblog. It also said vessels were not allowed to enter the central port zone, which is near the blast site.

The municipal government, which gave the death toll of at least 50, said 701 people were injured, including 71 in serious condition. The Tianjin Port Group Co. said dozens of its employees were unaccounted for and a search is under way. Some migrant workers at the port may not be documented.

Authorities said the blasts started at the warehouse owned by Ruihai Logistics, a company that says it stores hazardous materials including flammable petrochemicals, sodium cyanide and toluene diisocyanate.

An initial explosion apparently triggered an even bigger one. The National Earthquake Bureau said the first blast was the equivalent of 3 tons of TNT, and the second 21 tons. The enormous fireballs from the blasts rolled through a nearby parking lot, turning a fleet of 1,000 new cars into scorched metal husks.

Zhang Siyu, who lives several miles from the blast site, said she ran from her home without her shoes because she initially thought it was an earthquake.

"Only once I was outside did I realize it was an explosion. There was the huge fireball in the sky with thick clouds. Everybody could see it," she said.

Zhang said she could see wounded people weeping. She said she did not see anyone who had been killed, but "I could feel death."

State media said senior management of the company had been detained, and that President Xi Jinping demanded severe punishment for anyone found responsible for the explosions.

There was no immediate sign of any toxic cloud in the air as firefighters brought the fire largely under control by morning. However, the Tianjin government suspended further firefighting to allow the team of experts to survey hazardous materials at the site, assess dangers to the environment and decide how best to proceed.

In a sign of sensitivity over the hazardous materials stored at the warehouse, state broadcaster CCTV went live to a news conference in Tianjin when the head of the municipality’s Environmental Protection Bureau chief, Wen Wurui, was speaking. He said there had been no apparent impact on air monitoring stations, but that water samples were still being examined.

When a reporter asked him whether the chemicals at the warehouse had been stored far enough away from residences and Wen seemed at a loss for a response, the broadcaster suddenly cut away, only to return to it later.

Police kept journalists and bystanders away with a cordon about a mile the site. On China’s popular Weibo microblogging platform, some users said their posts about the blasts were deleted, and the number of searchable posts on the disaster fluctuated, in a sign that authorities were manipulating or placing limits on the number of posts.

The Tianjin Internet Police, on their official microblog, warned social media users to stick to official reports about the number of dead and injured, saying that there would be "zero tolerance for creating rumors."

The website of the logistics company became inaccessible.

The Tianjin government said that because of the blasts it had suspended online access to public corporate records. It was not clear whether the blackout was due to technical damage related to the explosion. No one answered the phone Thursday at the Tianjin Market and Quality Supervision Administration or the Tianjin Administration for Industry and Commerce.

Ruihai Logistics said on its website — before it was shut down — that it was established in 2011 and is an approved company for handling hazardous materials. It said it handles 1 million tons of cargo annually.

Photos taken by bystanders and circulating on microblogs showed 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 sky bright orange, with tall plumes of smoke.

About 1.2 miles 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 the explosion. Like surrounding buildings, the Mediterranean-style complex had all its windows blown out, and some of 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 of 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 only his surname, Li.

Tianjin, with a population of about 15 million, is being promoted by the Chinese government as a center for finance and high-tech industry. The Tianjin Economic Development Area has attracted foreign investors including Motorola, Toyota, Samsung and Novozymes.

The port has grown in importance as companies wanting lower manufacturing costs have migrated to the north from eastern and southern China’s manufacturing centers.

In the U.S., the White House sent its condolences, with spokesman Ned Price calling the explosions a tragedy and praising the first responders working to help the injured.

Associated Press writers Ian Mader, Didi Tang and Joe McDonald in Beijing, Erika Kinetz in Shanghai and Josh Lederman in Washington contributed to this report.