Asian stock markets opened sharply lower today after Italy's record-high cost of borrowing renewed fears over the Euro-zone crisis. Japan's Nikkei index fell 2.8%, South Korea's Kospi shed 3.7% while Hong Kong's Hang Seng dropped 4.4%.The falls in Asian markets follow losses in US markets.The cost of borrowing on Italian government bonds jumped to 7% on Wednesday, a level considered unsustainable by economists.Shares of banks in both Japan and Australia were hit particularly hard.In Tokyo, Sumitomo Mitsui Financial Group tumbled 5.3%, while Mizuho Financial group fell 3.8%.In Sydney, Westpac Banking Corporation dropped 3.6%, to its lowest level in a month.