China’s commercial banks have begun asking clients to submit “proof of use” for consumer loans, as the government tightens regulations on concern that such loans are being used to buy property and are helping to fuel a property bubble.

Customers of China Merchants Bank (CMB) with loans upwards of CNY10,000 are being requested by text messages to submit proof of use. Media reports said customers of some banks are required to prove that loans were not being used inappropriately. Household short-term loans soared in the third quarter by CNY1.53 trillion, almost three times more than a year ago, according to the People’s Bank of China (PBOC).

“I am afraid a considerable part of consumer loans has flown into the property market,” said ING Economist Iris Pang. “If you look at the structure of the consumer loans on the mainland, you will find it strange because a lot of them have extremely long loan tenures, like 10 to 20 years. What makes you need 20 years to pay back a consumer loan that enables you to buy a television? It is very likely that the money is spent on houses,” she said.

The China Banking Regulatory Commission (CBRC) announced it would investigate the fast build up of loans in the household sector and said last month that China should “learn from the subprime mortgage crisis in the U.S.”.