"BlackBerry has not engaged in discussions with Samsung with respect to any possible offer to purchase BlackBerry," the company said in a statement. "BlackBerry's policy is not to comment on rumors or speculation, and accordingly it does not intend to comment further. "
Later Wednesday, Samsung also denied making a takeover offer.
BlackBerry ended the session about 30 percent higher a Reuters report that Samsung had offered to buy the Canadian mobile company for as much as $7.5 billion, in hopes of gaining access to its patent portfolio, according to a person familiar with the matter and documents seen by Reuters.
Reuters stood by its previous report and said executives from both companies met last week to discuss a potential transaction.
Separately on Wednesday, Canadian newspaper Globe and Mail reported BlackBerry has shunned a handful of takeover overtures in recent months as its board and largest investor think its restructuring strategy will deliver greater shareholder value than current acquisition offers.
BlackBerry shares closed at $12.59, its highest stock price since June 2013, making its the company's best day in more than 11 years.
The stock gave back much of those gains after BlackBerry shot down the Samsung report. It was last trading below $11 per share, down about 16 percent in after-hour trading.
Samsung's strength as the No. 1 global smartphone marker has been built on making devices for the consumer market, which has become crowded in recent years. With a takeover of Blackberry, Samsung could make greater inroads into the corporate market, where it has trailed rivals.
Reuters contributed to this report.