To keep paying the mortgage or not? This question has been bugging 28-year-old Chen Jie for a month now.

The price of the two-room apartment she bought in September, located in Shenzhen's Nanshan district, has fallen by nearly 200,000 yuan, down from 11,000 yuan per sq m to 8,200 yuan per sq m.

"The market value of this property has fallen by more than my first installment of 158,400 yuan," says Chen, who is seriously considering giving up the apartment and buying another one on the cheap.

But she also knows clearly the consequences of defaulting on the mortgage: a smudge in the credit record that in turn could mean no credit cards in the future and possibly no more loans either. "I really don't know what to do. But if property prices fall further, I might have to give up the apartment," she says.

Like Chen, some domestic banks are just as antsy. What worries them is that many of their clients are asking themselves the same question as Chen, and coming up with "yes" as the answer. Statistics from Shenzhen Real Estate Research Institute show Shenzhen's property prices dropped 36 percent in May from the peak last year, indicating growing mortgage risks.

Feng Yu, a Shenzhen-based real estate insider, says in his blog that over 300,000 Shenzhen mortgage lenders have seen their asset prices fall and that the scale of Shenzhen banks' potential bad loans could be as high as 100 billion yuan.

"That's far from true. As of May, Shenzhen local banks had outstanding mortgage loans of 220 billion yuan," says a manager at a local bank's credit department who declines to be named. "It's considered bad loan if mortgage payment is not made for 90 straight days."

Shenzhen Banking Regulatory Bureau said on July 25 that local banks' non-performing ratio stood at 0.63 percent by July, down 0.2 percentage points than the beginning of this year.

Most bankers decline to comment, saying "it is a very sensitive moment". Song Liang, marketing chief of China Financial Services Group Limited (Shenzhen branch), a financial intermediary that mainly helps banks to manage mortgage for pre-owned houses, says there are more people deciding not to pay their mortgage this year compared with the last but the number is not as big as some media reports have put it.

"Most people who stop paying mortgages are speculative investors rather than those buying apartments for their own use," Song Liang says. "In fact, property prices in Shenzhen's urban areas don't drop much because of the limited supply and good quality."