Korea's central bank raised a key interest rate by 0.25 percent to 5 percent on Thursday, the highest level in six years.

The unprecedented and unexpected second straight monthly hike by the Monetary Policy Committee was made amid concerns about excess liquidity and increasing inflation.

Analysts had predicted that the interest rates would remain the same.

The Committee also raised the interest rates on both the Bank of Korea's Liquidity Adjustment Loans and Aggregate Credit Ceiling Loans by 25 basis points to 4.75 percent and 3.25 percent, respectively.

South Korea's economy grew at a higher-than-expected rate of 4.9 percent for the second quarter, which ended June 30, compared to the year ago period.

Inflation