Pikachu was welcomed home by thousands of enthusiastic gamers Friday as the global phenomenon of Pokemon Go finally launched in Japan, extending a wildly successful franchise that is part of the national social fabric.

The smartphone app has now been launched in more than 40 countries, including the US and much of Europe, but Japan -- where Nintendo started the mythical creature franchise 20 years ago -- was kept waiting.

The suspense lasted for days, as international media reports about a timeline for the Japan rollout kept changing, and Nintendo, the Pokemon Company, and the game's US-based developer Niantic all declined to comment.

But that finally ended Friday as the game was made available online in Japan.

"We are truly happy that we have been able to bring this to Japan, where Pokemon was born," Niantic announced on its blog.

It attributed the delay in Japan to responses "beyond our expectations" after the game's rolling release began on July 6.

User reaction in Japan was ecstatic.

Sixteen-year-old high school student Mamiko Amaha was immersed in Pokemon Go with a group of girlfriends in Tokyo's historic Asakusa district in search of Pokemon characters, as crowds of tourists strolled around.

"It was like, 'Finally! I want to play it immediately,'" Amaha said outside colourful Sensoji Temple of her reaction when the app became available.

"When we're playing, we see Pokemon on our friend's shoulder," she added. "So we're like, "It's there, it's there!"

Her friend Maika Kubo, also 16, admitted to being a bit perplexed at playing the game. But that didn't dampen her enthusiasm.

"I'm not really familiar with Pokemon, but it's fun," she said.

Since its global launch, Pokemon Go has sparked a worldwide frenzy among users who have taken to the streets with their smartphones.

The free app uses satellite locations, graphics and camera capabilities to overlay cartoon monsters on real-world settings, challenging players to capture and train the creatures for battles.

- 'Cannot bother' -
Pokemon, short for "pocket monsters" has been a constant in Japan since first being launched as software in 1996 for Nintendo's iconic Game Boy console.

It expanded into other media, most notably a wildly popular TV animation show and its popularity has never waned.

Tsunekazu Ishihara, president of Pokemon Company, told top-selling daily Yomiuri Shimbun in February that the secret of its popularity was rooted in social exchange as it has allowed for "trading Pokemons among friends".

Indeed, 27-year-old Tsubasa Kawaguchi, playing the game on his smartphone outside a McDonald's in electronics gadget-haven Akihabara, has grown up with the phenomenon.

"People of my generation have been playing Pokemon games," he said.

Now, Pokemon Go has given a shot in the arm to Nintendo's nascent move into mobile gaming -- after it abandoned a longstanding consoles only policy.

The videogame giant's stock at one stage had more than doubled from its July 5 close, sending its market value soaring as investors saw the app's popularity as positive for the company's mobile gaming strategy.

McDonald's Japan and Pokemon Company, meanwhile, officially announced a collaboration whereby the fast food chain's outlets will be key locations -- gyms and PokeStops -- for Pokemon Go players.

Though a verifiable global phenomenon, authorities in a number of countries have expressed safety and other concerns about the craze.

Indonesian civil servants, for example, have been ordered not to play Pokemon Go at work in a bid to protect "state secrets", according to a government statement Thursday.

And amid widespread anticipation before the release in Japan, the government issued a rare safety guide warning over dangers gamers could face, from heat stroke to online scams.

The country's Nuclear Regulation Authority also issued a warning on Thursday, calling on atomic power plant operators to watch out for Pokemon Go players who might approach facilities while playing the game, an agency official told AFP.

Another potential pitfall could be Pokemon Go's effect on workplace discipline.

"Pokemon Go came, I cannot bother with work," a Twitter user posted minutes after it hit Google Play in Japan.