"The coastguard is flying a plane to the area and a patrol ship is heading there too," a spokesperson told AFP. "But we haven't been able to confirm the safety of the seven members."
11 Indian crew missing after vessel sinks off Philippines: Japan
The capsized Japanese boat was found earlier in the day 410 kilometres (250 miles) southwest of Palau after the crew sent an SOS on Monday.
Nearby vessels including a ship from Japan's National Fisheries University joined the search and Japan had asked Guam for cooperation, the spokesman added.
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