Over 800 people rescued after the flash flood, 910 remain missing, say authorities; alert sounded along Bhotekoshi river as satellite images show blockage upstream; probe on to determine the role of glacial lakes in the devastating flood, says Nepal; 517 foreign nationals unaccounted for; Nepal PM Balendra Shah reaches nearest motorable town Over 800 people rescued after the flash flood, 910 remain missing, say authorities; alert sounded along Bhotekoshi river as satellite images show blockage upstream; probe on to determine the role of glacial lakes in the devastating flood, says Nepal; 517 foreign nationals unaccounted for; Nepal PM Balendra Shah reaches nearest motorable town