Sentiment among South Korean big businesses fell to a six-month low as the already fragile domestic demand weakened further after the deadly ferry disaster, a local business lobby survey showed Tuesday.

Business survey index (BSI) for August, a gauge of business environment outlook for the upcoming month, fell to 91.6 from the prior month's 94.0, according to the Federation of Korean Industries (FKI). It marked the lowest in six months.

The index was based on the survey response from the country's 600 largest companies by sales. A reading below 100 means pessimists outnumbered optimists.

The dimmer outlook came as consumer confidence continued to worsen after the ferry Sewol capsized and sank off the southwestern coast on April 16.

The accident, one of the country's worst maritime disasters, left more than 300 people, mostly high school students, dead or missing. Consumers refrained from travel and entertainment as deep grief swept over the entire country.

Private consumption declined 0.3 percent in the second quarter from three months earlier, marking the lowest in 11 quarters. Sales in major discount chains and department stores fell 5.9 percent and 4.6 percent in June from a year earlier.

Consumer confidence on future economic situations tumbled to the lowest in 15 months in July, and operating profits for Samsung Electronics and Hyundai Motor, the country's top two companies, dropped 24.5 percent and 13.3 percent each in the second quarter on a yearly basis.

Real gross domestic product (GDP) increased 0.6 percent in the second quarter from the prior quarter, logging the lowest growth in seven quarters.

Kim Yong-ok, head of the FKI's economic policy team, said that the prolonged aggravation of domestic demand and consumer sentiment led to the worsening of business confidence.