GENEVA, Switzerland(AFP)—More than 50,000 people are missing after powerful twin earthquakes rocked Venezuela, the United Nations' aid chief said Friday, warning that the death toll was likely to "rise significantly". "It's a very, very complex emergency response," Tom Fletcher, the UN Under-Secretary-General for Humanitarian Affairs and Emergency Relief Coordinator, told AFP in an interview. "We've got over 50,000 people missing, over 500 people dead, so a massive job to go through the rubble".