With pressure building on the 10th day of the Mosul assault, Western defence chiefs were already looking ahead to the next target -- IS's other major stronghold of Raqa in Syria.
The Hang Seng Index in Hong Kong sank 1.15 percent, or 268.81 points, to 23,056.62.
The cause of the blast was not known.
The quake, at a shallow depth of 10 kilometres (six miles), struck shortly after 2:00 pm (0500 GMT) in Tottori prefecture.
Taking a break from the nastiest campaign in recent memory, Donald Trump and Hillary Clinton came together Thursday for a New York white-tie soiree intended to bring some levity just weeks before the November 8 vote.