By Caroline Valetkevitch

NEW YORK Shares of home and kitchen product maker Tupperware extended their sharp, unexplained gains on Thursday, rising about 50% and putting the stock up more than 300% during the last five trading days despite recent concerns about its business.

The manufacturer's stock rose as high as $3.75, its steepest level since early March, and was last up 52% at $2.88 in mid-afternoon trading on Thursday. Trading volume was also well above average for the company and reached more than seven times the stock's 10-day moving average.

The stock gains have come despite signs earlier this year of problems for Florida-based Tupperware Brands Corp. In April, it raised doubts about its ability to continue amid growing concern amid weak sales, while in May it said it signed on investment bank Moelis & Co to help explore strategic alternatives.

It also said that it had found additional prior period misstatements in its financial reporting.

Tupperware's stock on Thursday was also among the most watched tickers on retail-investor-focused Stocktwits.com, with an "extremely bullish" sentiment score.

The sharp, unexplained gains echo those seen in Bed Bath & Beyond before it filed for bankruptcy and other "meme" stocks known for their sudden popularity with retail investors.

Also like other "meme" shares, Tupperware's stock is highly shorted. About 25% of the company's public float was sold short as of July 14, according to Refinitiv data.

Investors who sell securities 'short' borrow shares and then sell them, expecting the stock to fall so they can buy the shares back at the lower price, return them to the lender and pocket the difference.

Even with the recent gains, Tupperware's stock is down about 30% for the year to date.

(Reporting by Caroline Valetkevitch; editing by Susan Heavey)