geneva bangladesh border guard report 11,000 rohingya refugees cross country myanmar monday sudden surge unite nations refugee agency say half million rohingya flee myanmar since aug. 25 insurgent attack security force trigger violent government crackdown rate slow 2,000 refugees per day last week aid agencies say back situation full alert far influxes concern big increase see 11,000 adrian edwards spokesman u.n. high commissioner refugees unhcr tell news brief geneva tuesday big number come across day six weeks emergency back approach peak arrivals clearly prepare arrivals say many refugees report come buthidaung area myanmar northern rakhine state 20-25 kilometers east maungdaw say flee torch kill back home one boy see big gash across neck edwards say know moment drive add people flee home several days ago case two weeks ago move toward border come across also indications recent problems may see media report verify report fire see close border problems edwards say meanwhile massive cholera immunization campaign begin tuesday near cox bazar bangladesh aim protect newly-arrived rohingya host communities disease deadly world health organization say 900,000 oral vaccine dose distribute include 650,000 initial 10-day campaign follow second round oct. 31 target 250,000 children one five years old agency say clear present risk spread cholera among population luckily confirm case cholera far spokesman christian lindmeier say unhcr 'full alert 11,000 rohingya flee day