PEOPLE are catching imaginary monsters at Martyrs' Memorial and other popular Oxford landmarks after a new mobile phone app was launched in the UK.

Pokémon GO became available yesterday, meaning users can view the computerised Japanese monsters through their smartphone cameras as they walk around.

The app uses GPS to track where you go and alerts you to Pokémon (the monsters) and their haunts – known in the game as Pokéstops and Pokémon gyms.

Based on real landmarks and buildings, in Oxford these include Martyrs' Memorial in St Giles, Blackwells Music Shop in Broad Street and the statue of William Herbert at the Bodleian Library.

Puzzled security staff at the Bodleian yesterday confessed they couldn't tell people using the app apart from the usual throngs of tourists.

A Twitter account telling avid players where to go, said Pioneer Square in Bicester was a popular destination.

Many people eager to play the game had already downloaded it before yesterday by accessing it from other countries.

The Oxford Mail tried the app in Oxford city centre and found 17-year-old Max Lawson playing at Martyrs' Memorial, where he had placed a virtual 'lure'.

The lure, which lasts 30 minutes, attracts Pokémon in the game – and also other players.

Max, a former pupil at Oxford City College, said he had walked almost 40km because of the game over three days and spent £80 on optional in-game purchases.

He said: "It's a brilliant game that really gets you out and moving.

"I've been playing it for a few days and have seen loads of other people doing it as well.

"There are a few I've talked to and added on Facebook."

This week concerns were raised about the app by the NSPCC, which says it may cause children to wander around on their own.

It was first launched in Australia and New Zealand, and in the US has become more popular than the dating site Tinder. It is available for free on the iOS App Store and from Google Play.

A spokeswoman for Thames Valley Police advised people to keep phones "out of sight when in public places".

She added: "Using your mobile phone in public can make you an easy target for a thief. A mobile phone is stolen in half of all robberies and a mobile phone is the only thing that’s stolen in a third of all robberies.

"Stay alert, be careful when crossing the road, don’t trespass on private property and avoid dangerous locations or places like poorly-lit alleyways and car parks.

"Never use your phone while driving as this is illegal."

More information for parents is available about Pokemon GO at getsafeonline.org/news/pokemon-go-what-you-need-to-know