It marks the largest on-year gain in nearly seven years since the number expanded 9.9 percent on-year in the third quarter of 2010.

Their income from business activity shrank in the second and third quarters of 2016 before recovering to a 0.85 percent increase in the final quarter of last year.

The first-quarter rise was attributed mainly to an improvement in the domestic property market, which led to a surge in their lease income.

"Despite the overall sluggishness of the economy, the high-earning households posted a marked increase in their rental income, which helped boost their business income," a government official said.

The total monthly income of the top 20 percent rose 2.5 percent on-year to 9.29 million won in the first quarter on the back of the sharp increase in business income. Their earned and property income also gained 2.4 percent and 37.3 percent, respectively.

In contrast, the lowest 20 percent in the income bracket saw their total monthly income fall for five straight quarters to 1.39 million won, affected by continued corporate unwillingness to hire amid a prolonged business slump.

The average monthly income of all households in South Korea, meanwhile, edged up 0.8 percent to 4.59 million won in the first quarter. The slight gain was ascribed to the first drop in their earned income in seven years. (Yonhap)