Smoke and fire are seen after an explosion in the Binhai New Area in north China's Tianjin Municipality on Aug. 13, 2015. [Xinhua/Yue Yuewei]

TIANJIN, Aug. 13-- Several containers caught fire before the warehouse explosion at Tianjin Port on Wednesday night, authorities said on Thursday.

Firefighters arrived at the port at around 11:06 p.m. following a report that containers were on fire, said Zhou Tian, head of Tianjin's public security bureau's fire department at a press conference on Thursday afternoon.

However, authorities said the cause of the blast is still under investigation.

Another batch of firefighters arrived at around 11:16 p.m., according to Zhou, roughly 14 minutes before the first warehouse blast occurred.

The blasts, massive enough to register as seismic activity, left 44 dead, including 12 firefighters, and 521 people hospitalized, including 52 critically injured.

So far more than 1,000 firefighters, 151 fire engines and a drone have been dispatched to the blast site, Zhou said.