TOKYO (Reuters) -Mizuho Financial Group ( MFG ) reported a 62% jump in second-quarter net profit and lifted its annual guidance on Thursday, helped by strong lending demand and higher margins following a July interest rate hike by the Bank of Japan.

Japan's third-largest lender by assets reported a group net profit of 277 billion yen ($1.78 billion) for the July-September period, compared with 170 billion yen profit in the same quarter a year earlier. It lifted its full-year profit guidance to 820 billion yen from 750 billion yen.

Underscoring the bumper results, Mizuho said it would repurchase 50 million of its own shares worth 100 billion yen in a rare share buyback for the company. It lifted its annual dividend forecast by 15 yen from its estimate in May, to 130 yen.

The central bank raised its policy rate to 0.25% in July, pushing Mizuho's loan and deposit rate margin for its domestic lending business up for the second consecutive quarter.

Japanese banks' lending margins had suffered during seven years of negative interest rates, which ended in March.

Fellow megabanks Mitsubishi UFJ Financial Group and Sumitomo Mitsui Financial Group report results later on Thursday.

($1 = 155.8400 yen)