(NBC News) - Samsung has recalled 2.5 million Galaxy Note 7 smartphones amid reports some of their batteries exploded while being charged. Coming less than one week before Apple releases its latest iPhone, the record recall is a strike against the South Korean tech company, which saw billions of dollars removed from its share value this week. Shares rose after the recall was announced Friday morning.

In a statement released Friday, the tech giant said it would prepare replacement devices for those already sold. Retailing in the U.S. at around $850 per phone, the recall is a huge setback for the world's largest smartphone maker. It was not immediately clear when new sales of the devices would begin.

Samsung Electronics launched the Note 7 on August 19 in markets including the U.S.

South Korean high school teacher Park Soo-Jung told The Associated Press she rushed to buy the Galaxy Note 7, pre-ordering and then activating it on August 19.

The 34-year-old recounted by email that her phone later burst into flames, filling her bedroom with smoke smelling of chemicals.

An employee of a Samsung service center in Busan who visited Park's school to retrieve the scorched phone confirmed that her Galaxy Note 7 caught fire and said the sample was sent to the company's headquarters.

"If the exploded phone in flame was near my head, I would not have been able to write this post," she said in a popular online forum on Thursday, where she shared a photo of the scorched Note 7 and described dousing the burning phone with water.

It is unusual for Samsung to confirm a delay in sales of a device, and rare for it to cite a quality issue.

"Every year, there have been accidents of battery explosions but it is the first time that six or seven cases happened within such a short period after the launch of a new product," said Ha Joon-doo, an analyst at Shinhan Investment Corp.

The Galaxy Note 7 smartphone is the latest iteration of Samsung's Note series. It features a giant screen and a stylus.