Tianjin explosion: Dozens dead; areas of Chinese port city devastated

You can see the devastation everywhere: in the hollowed-out shells of barely-standing buildings, in the anguished faces
of relatives waiting for news of loved ones, in the parade of scorched cars.

But what was it that set off the terrifying blasts that ripped through warehouses containing hazardous chemical materials, sending fireballs shooting across the sky and shaking tall buildings more than 2 miles away?

Hours later, amid the destruction in this northern Chinese port city of more than 13 million, the exact cause of Wednesday night's blast remained unclear.

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