Justin Bieber Back in the Danger Zone -- Smoking Weed Onstage? (VIDEO)

10:15 AM PT -- It looks like there's some slight of hand going on in the video. At :11 ... Justin takes the joint in his right hand and then turns his back to the crowd. Here's where we can't see what happens with the joint, but when Justin turns back around at :16 ... he already has a white cigarette in his left hand, which he smokes.

We have no idea what happened to the joint. Where's Zapruder when you need him?

Justin Bieber has fallen off the wagon -- at least for a night -- because it appears he was smoking weed onstage ... one of the drugs that led to his DUI arrest and downward spiral.

Justin was performing in New Zealand with Rae Sremmurd, when he lit up a joint and puffed away.

He also took a big swig from a bottle of Hennessy.

The liquor isn't as alarming as the weed. Justin has never stopped drinking, though he insists it's never been excessive.

But marijuana is a different story. He was living in a constant haze during his low point, in large part because of pot. He was arrested for DUI in Miami last year and tested positive for marijuana.

We're told Justin regrets his New Zealand antics and did it on a dare, but there are pretty clear warning signs.