A crazed man went on a public rampage in Taipei, Taiwan Friday, leaving at least 3 people dead and multiple people injured Friday … and video shows the terrifying street scene.

Watch the video … an unidentified man wearing black clothing crouched down in a Taipei intersection, opens a backpack and started tossing smoke grenades, causing confusion near a train station. Then he pulls out a long knife and trots over to a sidewalk, where he begins stabbing and swinging at pedestrians … then makes his way into the front entrance of a building.

The panicked crowd on the sidewalk scatters, and people inside the building begin streaming out the doors moments after the attacker runs inside.

Reuters reports the suspect died after falling from a building being chased by police. The suspect was not publicly identified, but officials said he had a criminal record and outstanding warrants. His house was in the process of being searched Friday night local time.

Nick Reiner was diagnosed with schizophrenia, and in the weeks leading up to the murder of his parents, Rob and Michele Reiner, the meds he was taking made him “erratic and dangerous” … TMZ has learned.

Two sources with direct knowledge tell TMZ … Nick was under the care of a psychiatrist for mental illness. We’re told in the month before the murders, Nick’s behavior had gotten “alarming.”

He had recently received care at a Los Angeles-based rehab facility that specializes in mental illness and substance abuse. We’re told the facility charges $70,000 a month … and lots of rich, powerful parents send their troubled kids there.

Before ya guzzle down a bunch of holiday treats over the next few days, here’s Cristiano Ronaldo reminding folks what’s possible with a ton of discipline and living in the gym.

The 40-year-old international soccer star went to social media to show off his Greek god-like bod on Friday … telling his 105 MILLION X followers he just hopped out the sauna — and, lucky for us, providing visual proof.

The Al Nassr striker rocked nothing but black briefs and slides for the photo op … making sure his chiseled abs and veiny legs were on full display.