TIANJIN, China (AP) — A port company says dozens of its employees are unaccounted for in the aftermath of the fiery explosions at a warehouse of hazardous chemicals in a Chinese port city. The company says a search is under way.

The official death toll stands at 50, with more than 700 injured. The explosions shortly before midnight Wednesday night demolished a workers' dormitory, and tossed shipping containers as if they were toy blocks. Windows were shattered for miles around.

There's no indication yet of what caused the disaster in one of China's busiest ports. Authorities are trying to keep a tight rein over information by keeping reporters far from the site.

Social media users say their posts about the explosions have been deleted.

Authorities said the blasts started at a warehouse owned by a company that says it stores hazardous materials. 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.

More than 1,000 firefighters were sent to the area.