"The man said he wanted to keep (Knut) company," Berlin police spokeswoman Miriam Tauchmann told Reuters. "He was very lucky that nothing serious happened with such an act of foolishness."

Quick-thinking zookeepers threw Knut a leg of beef to distract the bear after the man, 37, waded through a moat and climbed into Knut's enclosure at Berlin's Zoo. Polar bears are among the fiercest animals in the world.

Knut, 2, who as a harmless little cub used to wrestle with his keeper, is now 220 kg (400 lb) and a predator. But this time he simply looked at the visitor impassively, then ate the beef.

The invader ignored zookeepers' orders to leave and only left when police arrived 20 minutes later and pulled him from the pen. The man was wet and cold, but unhurt. He was later released, but is expected to face a trespassing charge.