SAN FRANCISCO (CBS SF) – Police in San Francisco said at least one player of the suddenly popular Pokemon Go smartphone game has been the victim of a strong-arm robbery.

Officer Grace Gatpandan told KPIX 5 Tuesday afternoon that a suspect approached a person playing the game and stole the victim’s phone. No other details have been released about the incident.

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The augmented reality game, in which players scout real world locations to collect Pokemon, quickly became a national phenomenon after being released last week. Since the game’s release, Nintendo stock has soared, with shares going up nearly 25 percent on Monday.

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While the game has many people glued to their smartphone screens, crime has become a concern after police in Missouri said four teens used the game to rob players.

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On Monday, SFPD Captain Raj Vaswani issued a warning to Pokemon Go players, telling them to know their surroundings, obey all traffic laws and to avoid areas they wouldn’t usually go if they weren’t playing.

“If you get the sense you are being followed or set-up for a robbery, head to a lighted area with people around,” Vaswani said.

Injuries related to the game are also a concern, with players reportedly hurting themselves and walking into objects as they search for the so-called “pocket monsters.”

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The game was developed by San Francisco-based Niantic.