The number of corporate bankruptcies surged 20.9 percent in May from the year before to a three-year high of 1,310 due mainly to an increase in the number of small firms that failed, a private credit research agency said Tuesday.

But the debts left by those failed companies dived 48.2 percent to 368.57 billion yen, a 10-year low for May, because the number of large-scale bankruptcies leaving debts of 10 billion yen or more was limited to only three, compared with nine the year before, Tokyo Shoko Research said.

The monthly data cover firms going under with debts of 10 million yen or more.

The research agency said the number of small corporate bankruptcies, in which a failed company leaves debts of less than 100 million yen, rose 16.2 percent to 846, accounting for 64.5 percent of the overall failures.

Corporate bankruptcies have been at historically low levels in recent months thanks to the economic recovery and the government's financing programs to help small and medium-size firms, the agency said.

It remains unknown whether the number of bankruptcies has reversed the recent trend and regained upward momentum, it said.

Bankruptcies rose in eight of the 10 monitored industrial sectors. The eight were telecommunications, agriculture, forestry and fisheries, transportation, manufacturing, services, retailers, wholesalers, and construction.

In particular, bankruptcies were conspicuous among restaurants and automobile-related firms, including parts suppliers. Seventy-three restaurants failed while 34 firms in the auto-related industry went under. The number of employees affected by corporate failures totaled 11,347 in May, topping 10,000 for the third straight month.

Teikoku Databank, another research agency, separately released data that showed bankruptcies amounted to 1,016 in May, up 39.0 percent from the year before for an eighth month of increase.