SEATTLE, United States — Department store operator Nordstrom Inc said on Thursday that some members of the controlling Nordstrom family have formed a group to consider taking the company private as it struggles with an industry-wide slowdown in sales.

Shares of the company, which had a market value of $6.72 billion as of Wednesday closing, jumped as much 18 percent in their biggest intraday percentage gain since February 2009.

Rival department store stocks also rose. Macy's Inc was up 3.8 percent, Kohl's Corp 2.3 percent and J.C. Penney Co Inc 1.3 percent.

The group — which comprises chairman emeritus Bruce Nordstrom, his sister Anne Gittinger, president James Nordstrom and co-presidents Blake, Peter and Erik Nordstrom — has not made a formal proposal yet, the company said.

The group, which owns 31.2 percent of the company, said it was not interested in selling its stake to third parties or vote for an alternative deal.

Nordstrom, like other department stores, has reported weak sales in recent quarters as the industry struggles with a slump in demand for apparel and a shift to online shopping.

"Because of the changing dynamics in the retail environment, the group is evaluating whether the long term interests of the issuer (Nordstrom) are better served as a privately held company," the members of the Nordstrom family said in a filing.

The company's board has formed a special committee of independent directors to explore the possibility of any transaction that could be made by the group, which owns 31.25 percent of the company's shares.

The committee said it had entered into an agreement with the members of the Nordstrom family over some standstill provisions that would prevent them from taking certain actions until Jan 31, 2019.

The special committee has hired Centerview Partners LLC as its financial adviser and Sidley Austin LLP as legal counsel.

By Gayathree Ganesan and Siddharth Cavale; editor: Saumyadeb Chakrabarty.