Laura Dekker was in good spirits as she started sailing her 38-foot ship "Guppy" from the British territory bordering the southwestern tip of Spain, her manager, Peter Klarenbeek, said.
The attempt has been criticized by Dutch child protection authorities, who questioned the wisdom of a child risking the world's oceans alone. Dekker's departure itself was kept a secret from international media, who descended on Portugal but failed to capture images of it.
"She said goodbye to her father and friends and she sailed away into the horizon," said Holland's MasMedia company.
The girl is now en route to Spain's Canary Islands or Portugal's Madeira Island, depending on the wind, Schaaphok said. Then she plans to head through the Panama Canal to the Pacific Ocean, and on to Australia, the southern tip of India and through the Suez Canal en route to the Mediterranean.
Laura's Web site features links titled "My Coordinates" and "Where is Laura," but neither was working Saturday.
The trip comes two months after Abby Sunderland, a 16-year-old American, had to be rescued in the Indian Ocean during an attempt to circle the globe.