Chris Pratt looked like a legit action hero while filming a scene for his new movie -- and he's doing all his own stunts, it seems ... chasing a fictional bad guy into the Pacific Ocean.

The actor was spotted this week in costume and in character as an LAPD officer, shooting scenes up in Malibu -- which included one set piece that required him to chase a dude down into the sea, fully clothed mind you.

Chris was on the move in another clip too ... where he was seen holding out his gun and telling someone to get down. BTW, this movie he's filming is called 'Mercy,' and it's a sci-fi thriller where he plays a detective accused of a crime and needing to prove his innocence.

Despite playing the funny, fat sidekick in "Parks and Recreation," CP has transformed into a bona fide action star in the last decade ... and he's keeping that streak going in this flick.

Remember, Chris did a full body transformation to play a professional athlete in "Moneyball" and a Navy seal in "Zero Dark Thirty." Don't forget, Chris also became a Marvel superhero and led the "Jurassic World" franchise because of this new look.