PLANO, United States — JC Penney Co. shares tumbled the most since they began trading in 1980, hurt by deeper losses and a sense among investors that department stores are stuck in an intractable slide.

The rout followed a warning by the company that a massive inventory liquidation would bring a flood of red ink in the third quarter, renewing the sense that department stores are losing ground to e-commerce. The shares fell as much as 25 percent in the wake of the forecast.

The move spotlighted key problems for the department-store field: hard-to-sell inventory and a reliance on deep discounts to move stock. JC Penney also has been shuttering poor-performing stores in a bid to better match supply with demand.

“We took the necessary steps to accelerate inventory liquidation primarily across all apparel divisions, which increases available funding to invest in new and trending merchandise categories,” chief executive Marvin Ellison said. He pledged a “sharper and more disciplined focus on inventory management.”

JC Penney now expects to report a loss of 40 cents to 45 cents a share in the third quarter, when excluding some items. That’s deeper than analysts’ estimate of an 18 cent-per-share loss. The company will release results on November 10.

The whole industry faces “intense” headwinds from dwindling mall traffic, Jefferies LLC analyst Randal Konik said in a note. “The shift to e-commerce should also continue to weigh on profitability.”

The retailer said on Friday that it’s embarking on a “comprehensive reset” of its apparel inventory by liquidating less popular items. While the effort will lead to a comparable-store sales gain, it was a costly endeavour, resulting in a loss last quarter.

The shares fell as much as 25 percent — the biggest intraday plunge ever — to an all-time low of $2.76. The stock has lost 56 percent of its value in 2017 and 95 percent over the last 10 years.

Department stores have been particularly hard hit by a shift in consumer preferences, with shoppers eschewing malls for e-commerce and favouring non-traditional, upstart brands. JC Penney and its competitors have laid off workers and are reducing store counts while beefing up online operations to adapt to the new landscape.

JC Penney expects to see a bump of 0.6 percent to 0.8 percent in same-store sales in the third quarter, in part due to the clearance of inventory. Analysts have forecast an increase of 0.4 percent.

The company also is making changes to give a team overseen by chief financial officer Jeffrey Davis more leeway on pricing and planning. Davis assumed the post in July.

The inventory overhaul led to improved performance in the quarter, particularly for women’s apparel, the company said. It also cited appliance sales and omnichannel — a move to meld online and offline channels — as performing well.

“Although these actions will create a short-term negative impact to cost of goods sold and earnings, long term, we firmly believe it was the right decision for the company,” Ellison said.

By Jonathan Roeder; editors: Nick Turner and Jonathan Roeder.