SAO PAULO              -              At least 18 people were killed when a riverboat sank in the Amazon rainforest re­gion, Brazilian authorities said Monday, as survivors described fleeing the foun­dering boat in terror. The ferry was taking passengers up the Jari River, a tributary of the Amazon, when it sud­denly began to tip over on Saturday at around dawn. Authorities said late Monday that beyond the 18 fatalities, they had rescued 46 survi­vors and 30 others were still missing -- meaning there were far more people on board than initially believed. Search operations were ongoing, using helicopters, planes and rescue divers. The Brazilian navy said it had opened an investigation into the accident, the cause of which was unknown.