US banks left loan standards unchanged on commercial and industrial loans to large and mid-sized firms during the second quarter and eased standards on such loans to smaller firms, according to a survey of bank officers published on Monday.

The US Federal Reserve's quarterly survey of senior loan officers also showed there appears to be an overall easing of standards on commercial and industrial loans compared with before the financial crisis.

"Banks, on balance, reported that their lending standards on C&I loans are currently at the easier end of the range of standards between 2005 and the present," the report said.

That is notable because a rise in US business debt to historic levels has raised red flags at the US central bank over financial stability vulnerability.

Fed Chair Jerome Powell has said he does not see high corporate debt as posing the same sort of systemic threat that the subprime mortgage market did. But he has warned that further increases could be problematic.

The survey showed demand for commercial loans from larger firms in the second quarter was mostly unchanged, but the details suggest an improvement: among the minority reporting a change in demand there was a decline in the portion seeing a weakening, and an increase in those seeing strong demand, compared with the first quarter. Demand from small firms overall was weaker, the report said.

For households, the picture was somewhat different.

In the second quarter, banks tightened standards on credit card loans, the report showed, while they left standards for auto loans and most categories of real estate loans "basically unchanged" during the period. Demand for most household loans rose, the survey showed.

Longer-term, standards for commercial and real estate lending, as well as subprime credit card and auto loans, has tightened compared with what has been the norm from 2005 to now, the survey showed.