The app, which was first launched in Australia and New Zealand before overtaking Tinder in the US in popularity, has now appeared on the iOS App Store and Google Play.
The launch has been accompanied by a string of safety concerns because of the exploration nature of the game and how that could be exploited by criminals.
The children’s charity said in a statement: “It’s deeply troubling that the app’s owners have ignored many warning signals and well documented child safety concerns.
“It would have been better if they had taken time to reflect on these and put their young users first. Pokemon Go is setting a precedent as the most successful reality game app on the market. It’s very disappointing that child safety isn’t at its heart.”
The statement comes after the group urged the game’s developers on Wednesday to reassess the safety features of the game.
The charity said it is concerned that “basic safety standards appear to have been overlooked”.
The NSPCC said it is worried that offenders could target unsuspecting children by using the app’s geolocation feature.
Police in the UK have also begun to express concerns over player habits and the gatherings they can create.
Officers in Bury St Edmunds, Suffolk, tweeted on Thursday morning: “Last night four youths acting suspiciously in the town centre #burystedmunds ended up that they were playing #PokemonGO at 2 in the morning.”
Despite the game not being available in Britain until now, thousands of players in the UK have already downloaded the app by changing their region settings or using unofficial app stores, a move which also led to warnings of malware from security experts.
Nick Summers from technology site Engadget said the exploration aspect of the game should be praised, but agreed it should also come with a warning.
“It’s a fun, if shallow game that encourages people to go outside and explore their surroundings. In that regard, Niantic and The Pokemon Company should be commended,” he said.
“But there are dangers in the real world, and as the NSPCC said yesterday, it’s important that the right safety features are in place. For younger players especially, the usual advice applies here - be careful where you go and who you talk to.”