Witnesses said the death toll in the massive explosion that rocked the Chinese city of Tianjin has climbed to 50.

Twelve of the dead are firefighters who showed up for an initial report of a fire at the Tianjin port.  The twin explosions that struck just after their arrival has sent more than 700 people to hospitals and 71 are reported in critical condition.

At least 30 firefighters are still unaccounted for in the aftermath.

Chinese officials would not give a cause for the blasts but admitted the firefighters were pulled out of the area until a team of chemical experts could assess the site.

The Xinhua news agency reported 217 nuclear, biological and chemical specialists are on the site.

“We haven’t got any formal announcement from local government,” local resident Tang Lei told NBC News. “All the information we got so far is from media or friends who are working in the field.”

The China Daily newspaper has reported officials with Ruihai Logistics, a company that was storing chemicals like sodium cyanide on the site, have been taken into custody for questioning by police.  The company received citations two years ago for improper storage.