Shares of fuel cell maker Plug Power Inc (PLUG.O), which hit a near five-year high on Tuesday morning, tumbled 35 percent in heavy afternoon trading after short-seller Citron Research said the fair value of the stock was 50 cents.
Plug Power's stock fell to $6.67 and was the most traded stock on the Nasdaq. Nearly 200 million shares had changed hands by 1510 ET.
Citron called Plug Power a "casino stock," one that "can trade twice its outstanding shares in a single day, while turning over its entire float on people gambling that they can find a buyer at a higher price." (r.reuters.com/kym57v)
The stock, which has climbed 5,860 percent in the past one year, has surged since the company said on February 26 it would supply its hydrogen fuel cells to Wal-Mart Stores Inc (WMT.N).
Short interest in Plug Power's stock is very high, jumping to about 16 percent of outstanding shares as of February 14 from about 11 percent as of January 31.
Short-sellers borrow shares and sell them, seeking to profit by returning them after buying them back at a lower price.
Shares of other fuel cell makers such as Fuel Cell Energy Inc (FCEL.O), and Canada's Ballard Power Systems Inc BLD.TO (BLDP.O) and Hydrogenics Corp (HYG.TO) (HYGS.O) have also been on a roll in recent months.
These stocks have gained since Plug Power announced the contract, as investors bet on rising demand for fuel cells, which offer a cleaner way to power vehicles such as electric buses and forklifts.
Plug Power will report fourth-quarter results on March 13.
FuelCell reported a smaller first-quarter loss on Monday as revenue jumped 22 percent amid growing demand for multi-megawatt fuel cell parks.
Ballard said last month it expected revenue to rise 30 percent to about $80 million this year.
FuelCell shares lost more than a quarter of their value by afternoon. Ballard's shares slumped 24 percent to $5.25, while Hydrogenics' stock fell as much as 13 percent to $29.27.
(Reporting by Sayantani Ghosh in Bangalore; Editing by Kirti Pandey)