Authorities in Nepal have warned of further flooding after heavy rainfall, as China sheds more light on the scale of the disaster in its Tibet region.Five days after floodwaters unleashed by a glacier collapse buried communities under thick mud, rescuers in Nepal were still struggling to reach devastated areas as the full extent of the destruction came into focus.“The disaster here is overwhelming,” Ferrin Cole, an operations director with the U.S.-based Crisis Response International, told NBC News on Sunday. “The flood that came down that mountain just wiped out cities. We’re going in as fast as we can to get…