TOKYO, April 6 (Reuters) - Japan on Thursday said rescue efforts were under way to locate any survivors after one of its military helicopters carrying 10 people crashed in the sea near Miyakojima, part of the country's southwest Okinawa island chain. The UH60 troop transport, commonly known as the Black Hawk, disappeared from radar tracking after leaving a Ground Self Defense Force base on Miyakojima, General Yasunori Morishita, the head of the GSDF, said at a press briefing. See here for a complete list of exchanges and delays