European stock markets tumbled at the start of trading Tuesday, hit by fresh fears for the eurozone crisis after Greece proposed a referendum on last week\'s EU debt deal. London\'s benchmark FTSE 100 index slid 1.71 percent to 5,449.62 points, Frankfurt\'s DAX 30 shed 3.37 percent to 5,934.54 points and in Paris the CAC 40 lost 3.11 percent to 3,136.27.