New mobile game Pokémon Go has become an overnight sensation with US fans but also played a role in armed robberies in Missouri, the discovery of a body in Wyoming and minor injuries to fans distracted by the app.
The "augmented reality" game based on the 1990s Japanese franchise surged to the top of Apple's app charts over the weekend.
Gamers use their mobile devices to find and capture virtual Pokemon characters such as cuddly yellow Pikachu at various real-life locations.
Five days after its release, the game now is on more Android phones than dating app Tinder, and its rate of daily active users was neck and neck with social network Twitter, according to analytics firm Similar Web.
Highlighting a dark side to its popularity, the game was used by four teenagers in Missouri to lure nearly a dozen victims into armed robberies, police and media reports said.
Police warned players to be vigilant when using smartphones and other mobile devices to search for characters in the game.
Pokémon fans have embraced their inner Ash Ketchum with Nintendo's new mobile hit, Pokémon Go.https://t.co/qDUyOM06EX— RTÉ News (@rtenews) July 12, 2016
"When you're involved in a game and not paying attention to what's going on around you, your situational awareness can go down," Greensboro, North Carolina police officer Ben Wingfield told local television.
Developed by Pokémon Company International, Niantic Inc and Nintendo Co Ltd, the game uses the GPS mapping and camera systems on players' devices.
"We encourage all people playing Pokémon Go to be aware of their surroundings and to play with friends when going to new or unfamiliar places," Pokémon Company International and Niantic said in an emailed statement.
Police in O'Fallon, a suburb of St Louis, said they arrested the four teenagers on Sunday after a robbery victim called police from a shop.
"Using the geo-location feature of the Pokemon Go app, the robbers were able to anticipate the location and level of seclusion of unwitting victims," O'Fallon police Sergeant Bill Stringer said in a release.
Social media buzzed with reports of players who suffered minor injuries from tripping and falling while distracted by their cell phones and minor incidents while driving and looking for Pokémon.
The game was the most downloaded free app on Apple's appstore while Nintendo's shares surged nearly 25% for their biggest daily gains in history after Pokémon Go's takeoff.
Shayla Wiggins, 19, was searching for a water-based Pokémon character near Riverton, Wyoming, when she discovered a body near a bridge, where a man is thought to have drowned in shallow water, according to media reports.
"I probably would have never went down there if it weren't for this game," Ms Wiggins told CNN.