Delinquent borrowers from South Korean non-bank financial companies are growing at a fast clip, data showed Tuesday, raising concern over the worsening of the country's household debt problem.

The number of delinquent borrowers, who are more than 30 days behind in their repayments, accounted for 5.6 percent of the entire credit card loan users as of May, up from 4.5 percent in January, according to the data from local credit appraiser NICE Information Service.

The corresponding figure for financing companies and savings banks stood at 8.2 percent and 14.9 percent each.

The proportion of delinquent borrowers from banks, in contrast, inched up a mere 0.1 percentage point to 2.3 percent in the same period, the data showed.

The delinquency rate of so-called "multiple debtors," who are saddled with more than three loans to both savings banks and private money lenders, is especially alarming, with the figure standing at 26.3 percent as of end-2011, according to the Financial Supervisory Service (FSS).

"Although its growth rate has slowed through April and May this year, it's still relatively high compared with the overall delinquency trend," Ko Seung-beom, chief of the FSS's financial policy bureau, told reporters at a press briefing.

"We're keeping tabs on it and trying to contain financial firms' excessive supply of loans that often cause unnecessary borrowing by households," Ko said.

The fast-growing delinquency rate at non-bank financial institutes come as banks have capped their household loans since the financial regulator began to impose restrictions on local lenders last year in a bid to curb mounting household debts that have been a major drag on the economy.

South Korea's household credit stood at 911.4 trillion won ($793.2 billion) as of end-March.

Market watchers said, however, stricter requirements to borrow money has sent the low-income group to borrow money from non-bank financial firms at much higher interest rates.

They pointed out that low-income families are inevitably hurt by a slowing economy and eased rules and greater benefits are needed to prevent the household debt problem from worsening.

"There is a need to take measures like lowering loan rates or adjusting repayment periods as the delinquency of the 'financially-vulnerable' is getting more serious," Park Deuk-bae, a researcher at Hyundai Research Institute, said. (Yonhap News)