A Tokyo zoo is frantically searching for an escaped penguin that scaled the walls to freedom.

The one-year-old Humboldt penguin was last seen swimming in the Old Edogawa river, which runs into Tokyo Bay, in the Japanese capital city, reported AFP.  

We first noticed the penguin might have fled when the director of a neighboring zoo e-mailed us Sunday, with a photo, said Takashi Sugino, an official from Tokyo Sea Life Park. Sugino said that it appears the small bird climbed over a rock twice its size.

Zoo officials are unsure how the bird actually managed to escape the enclosure that it shares with 134 other Humboldt penguins.

Of course it can't fly, but sometimes wildlife have an 'explosive' power when frightened by something. Maybe it ran up the rock after being surprised, said Takashi.

 On Monday, zoo officials were reportedly searching the area where the bird was last spotted, in hopes of recapturing it, said AFP.

It's a bit of a struggle to catch it when it is swimming, because it swims at a tremendous speed, Takashi said. We are hoping to catch it when it climbs up on land to sleep.