The blast was reported at about 5:30 p.m. in the Mickey's Toontown area of Disneyland, Anaheim police spokesman Sgt. Bob Dunn said.
Disneyland officials on the park's Twitter account called the explosion "a small bang," and said that "in an abundance of caution, the area was evacuated." They said they were working with local authorities.
Anaheim police investigated with assistance from an Orange County sheriff's bomb squad.
About two hours after the explosion the review was completed, the area was deemed safe and guests were allowed to return to Toontown, Disneyland said.
Park visitor Allen Wolf says he was about 20 feet from the blast, near Toontown's City Hall.
Wolf said "it sounded louder than a gunshot," but similar.
"I looked up. Everyone stopped and looked up," Wolf said. "Security surrounded the trash cans then told everyone they were evacuating."
He said the park's music never stopped playing.
Mickey's Toontown, designed to make visitors feel like they've entered an old-fashioned cartoon, "is an interactive metropolis full of topsy turvy architecture and screwy sculptures," according to the Disneyland website.