Story highlights The death toll has more than double to 44, state-run news agency reports

Dozens of firefighters are missing, it says

More than 500 people are reported injured, dozens of them critically

Tianjin, China (CNN) A series of huge explosions shook the northern Chinese city of Tianjin late Wednesday, killing at least 44 people and injuring hundreds more, according to officials and state media.

The cause was not immediately clear.

Liu Yue, a 25-year-old Tianjin resident, said she felt the first blast but didn't think too much of it.

"The second explosion was so powerful that I felt the entire 16-floor-building was shaking," said Liu, who lives about 4 kilometers (2½ miles) from the site of the blasts. "I thought it was an earthquake! I was extremely scared. I was afraid my family was in danger."

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The initial explosion erupted at a warehouse for a logistics company in an industrial area of the port city, according to Tianjin police. The company was identified as Tianjin Dongjiang Port Rui Hai International Logistics Co. Ltd.

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