Subprime borrowers are falling behind on their car loan payments at the highest rate in more than six years, and some bonds backed by these loans are vulnerable to getting downgraded, according to S&P Global Ratings.

Competition has spurred lenders to loosen standards and resulted in more delinquencies and default by people with weak credit, the ratings firm said. Subprime borrowers were behind by more than 60 days on about 4.85 percent of auto loans in August, the highest level since January 2010. The rate was 4.14 percent in August of last year, S&P said. For prime loans, delinquencies in August rose to 0.5 percent from 0.41 percent in the same month in 2015. The figures apply to loans that have been bundled into bonds.

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