Pokémon Go developer Niantic has confirmed that the game's first legendary Pokémon will be available to capture in the hit augmented reality mobile game this Saturday (22 July) at a special, ticketed event in Chicago.

Those attending Pokémon Go Fest, which will also be broadcast live on Twitch and YouTube, will be able to capture one of the eleven legendary Pokémon that have so far eluded players, with players around the world able to shortly after.

Niantic made the announcement with a new live-action trailer harking back to the game's announcement trailer back in 2015.

Explaining how it'll work in a post on the official Go site, Niantic reveals battles with legendary Pokémon will function in the same way as the recently-added raids, which tasks players with teaming up to take down powerful monsters.

Conquer the Pokémon and players can then attempt to catch it.

"While legendary Pokémon will help them take on the toughest Raid Bosses and Gym Battles, they're not willing to leave their Trainer's side, so they can't be left to defend Gyms," the post adds.

The game's first legendary Pokémon will appear at the event in Chicago during phase two of the day's activities.

Phase one involves players dictating a bonus reward benefiting players around the world with the number of Pokémon they catch of a specific type. So, if they catch lots of fire types, that will mean players are awarded with more in-game candy needed to power up and evolve.

Players around the world can in turn determine how long the bonus remains in effect for themselves by also catching Pokémon. If they catch enough during the aforementioned time slots phase two will be unlocked for those in Chicago.

This is when they'll be able to battle the first legendary Pokémon: most likely Mewtwo.

"If the Trainers in Chicago succeed in defeating the legendary Pokémon, that Pokémon will start appearing in Raid Battles around the world, after Pokémon Go Fest," reads the post.

The trailer (embedded above) also shows the five legendary bird-types: Articuno, Zapdos, Moltres, Lugia and Ho-Oh. It's not clear whether they will be made available worldwide, but it's certainly implied.

There are five more legendary Pokémon not seen in the trailer: Mew, Entei, Raikou, Suicune and Celebi.