San Francisco has become Gotham City to make the wish of a five-year-old superhero come true.
Miles Scott, aka Batkid, left the city's Union Square in one of two Batmobiles on Friday morning.
The vehicles - two black Lamborghinis with Batman decals - were surrounded by media and onlookers.
Police blocked off roads as they escorted Batkid on his first caper, rescuing a damsel in distress from cable car tracks.
The drive through city streets is part of a day of events organised by the Make-A-Wish Foundation to fulfil Miles' wish to be Batkid.
Miles was diagnosed with leukaemia at 18 months old and is now in remission.
He also captured the Riddler as he robbed a downtown bank.
Later in the day he saved the San Francisco Giants mascot Lou Seal, who had been kidnapped by the Penguin.
The San Francisco Chronicle distributed hundreds of special-edition newspapers with the headline, "Batkid Saves City", in Union Square.
The White House even sent out a tweet encouraging Batkid to "Go get 'em!" and in a video recording, President Barack Obama said, "Way to go, Miles! Way to save Gotham!"
After all the criminals were captured Miles received a key to the city from Mayor Ed Lee.
He was presented with chocolate, an FBI 'raid jacket' and a San Francisco Police Department cap.
Miles' mother, Natalie, told Make-A-Wish: "This wish has meant closure for our family and an end to over three years of putting toxic drugs in our son’s body.
"This wish has become kind of a family reunion and is our celebration of his treatment completion."
The city’s effort has created a huge stir on social media and posts on Twitter captured the positive mood.
"Well done @SFWish This is one of the greatest things I've ever seen," @dustinpenner25) posted.
"If you want your faith in humanity restored, just look at the hashtag #SFBatKid. This is awesome," @benwinslow wrote.