It has been 75 years since the liberation of the Auschwitz extermination camp by Soviet troops in the final months of the Second World War. Survivors and world leaders gathered at the site ahead of an official ceremony. The morning began with a wreath-laying ceremony to honor the victims. Some of the last remaining Auschwitz survivors courageously returned to mark the anniversary. The event is being hosted by Polish president Andrej Duda. Among the guests invited to today's official ceremonies are German President Frank-Walter Steinmeier and Israeli President Reu-ven Rivlin and dozens of world leaders.