Circus Trainer Mauled By 500-Lb Bear in Front of Horrified Children, On Video

Russian circus trainer Sergei Prichinich is lucky to be alive after his nearly 500-lb bear costar, named Donut , recently went full attack mode during a recent live show.

In a video making the rounds online ... Sergei and Donut are entertaining a crowd of parents and children, with the brown bear riding a hoverboard near her trainer in an enclosure.

The act soon goes horribly wrong ... Donut jumps off the hoverboard and sprints after Sergei, tackling the trainer and pinning him to the ground for over a minute -- to the horror of the crowd -- aggressively whipping its head back and forth as Prichinich calmly defends himself with a baton.

An employee standing outside of the cage intervenes with a long staff, poking Donut repeatedly, distracting the female bear enough for Sergei to regain his footing.

The situation could've been significantly worse if Sergei hadn't used the baton to keep Donut's jaws from chomping down on him.

Sergei, being a seasoned professional, continued on with the show as if nothing occurred ... wrapping up Donut's act before things escalated further.

Nikita Mikhailov , head of the Moretti Circus, confirmed the rest of the show continued without further incident ... and applauded Sergei for his handling of the situation.

CELEBS WITH EXOTIC ANIMALS

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Nikita said ... "This is an animal, and they can behave differently, they may not like something, they can express their emotions this way. Every trainer understands this."

Unsurprisingly, the attack has garnered the attention of animal rights activists ... who cite this as another example of why live animal acts should be banned across the globe.

STARS WITH BIG BEARS

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Ringling Brothers has even retired its own animal acts, returning to performing last year with only acrobats and other human entertainers.

As they say ... if you don't adapt, you die ... and potentially at the hands of an angry bear. Talk about a "grizzly" way to go!!!