UPDATE 22/7/16: Pokémon Go is now available in Japan and already hugely popular, fuelled by a pent-up demand for the app and 3000 sponsored Pokémon Gyms in the form of McDonald's' restaurants.

The launch had to be pushed back a day as word it was coming thanks to a leak (below) went viral, and The Pokémon Company feared it would need more servers to cope with the excitement.

Japan's government has also chipped in, with warnings from the National Centre of Incident Readiness and Strategy for Cybersecurity. The agency has asked fans to be safe while playing, and not to get heatstroke.

"I want people to abide by the warning so that people can play it on smartphones safely," said Chief Cabinet Secretary Yoshihide Suga has been quoted as saying.

This morning, even Sony Worldwide Studios' Shuhei Yoshida has been out playing: