The Avengers star, who portrays the ageless Marvel superhero on the big screen, set up the prank at Boston's Comicazi shop, where he encouraged unsuspecting fans to take part in an Escape Room-style challenge by talking to them through the Captain America doll.

The fan surprise was set up to promote Evans' new competition with, which offers participants the chance to take on an Escape Room adventure with the actor himself to raise money for Christopher's Haven, a Boston-based facility which provides temporary housing for families of hospitalised kids undergoing cancer treatment.

As part of the Comicazi set-up, the Hollywood hunk hid in a separate room, where he watched the action unfold and offered instructions, through the doll, on how fans could help Captain America take down fictional terrorist organisation Hydra.

In video footage of the prank, Chris drew the attention of customers by calling out, "Hey, you two. This is Captain America here and I need your help. Are you up for the challenge?"

After the fans accepted, he explained, "This may look like a standard comic book store but it's actually a secret Hydra base, and I need your help to take it down."

He then talked them through a number of missions, and upon successful completion, a back door in the store, leading the fans to the room where Evans is hiding, opened, allowing them the chance to meet the star in person.

At the end of the video, Chris told viewers, "Now that you've seen what escape rooms are all about, let's see if you have what it takes to get out of one. Enter to join me for the game of a lifetime..."

"We'll solve some puzzles, get some pizza, celebrate our success or mourn our failure. It happens," he says. "But win or lose, the best part is that every entry supports Christopher's Haven... Good luck!"

Sharing the footage on his Twitter account on Thursday (19Jan17), Chris added: "We had SUCH a fun time making this. We're gonna have even MORE fun in our own escape room! Enter now!"

Entries for the contest cost just $10 (£8) and the winner will be chosen at random after the competition closes 3 February (17).