Shares of P.F. Chang's China Bistro traded down more than 10 percent Wednesday on investor concern about falling same-store sales and a disappointing quarterly earnings report.

P.F. Chang's (NASDAQ: PFCB) was down $4.00 per share, or 10.19 percent, to $35.26, just above a 52-week low of $33.25 on Wednesday with heavy volume.

The stock had traded down as much as 12 percent on the day.

Janney downgraded the stock to neutral to buy, having some impact, but investors overall churned large volume in a predominantly sell mode Wednesday after P.F. Chang's said same-store sales 2.5 percent at P.F. Chang's restaurants in the previous quarter and 2.7 percent at the company's Pei Wei Diners in the previous quarter.

Also, earnings per share at P.F. Chang's fell to $0.40 from $0.55 one year ago. Analysts had expected $0.55 for this quarter, so the earnings drop was a significant miss by Wall Street's perspective.

Further dragging down P.F. Chang's stock was pessimistic outlook provided by the company.

"(P.F. Chang's) also expects to experience incrementally higher labor costs, and, as a result, anticipates that restaurant operating income will decline approximately 120 basis points compared to fiscal 2010. Overall, the Company now expects consolidated diluted earnings per share to range from $1.60 to $1.70 for fiscal 2011," the company said in a statement.

P.F. Chang's, based in Scottsdale, Arizona, operates 201 full service bistro restaurants, including P.F. Chang's China Bistro and Pei Wei Asian Diner.

The company was founded in 1996.