The helium balloon constructed by the Heene family travelled more than 80 kilometres after it broke free of its tethers on Thursday. (KMGH-TV/Associated Press)Criminal charges will be laid in the case of a Colorado boy who was reported to have been carried away in a homemade helium balloon, the Larimer County sheriff said Saturday.

Jim Alderden didn't say what the charges would be, but he did say the six-year-old boy's parents, Richard and Mayumi Heene, were not under arrest.

Late Saturday night, three Larimer County sheriffs showed up at the Heene home with a warrant and began searching the building.

Alderden previously said that if the balloon ordeal was a hoax, the parents could be charged with making a false report to authorities, a low-level misdemeanour.

"We were looking at Class 3 misdemeanour, which hardly seems serious enough given the circumstances," Alderden said Saturday.

"We are talking to the district attorney, federal officials to see if perhaps there aren't additional federal charges that are appropriate in this circumstance."

He said deputies were seeking a search warrant for the family's home, and there would be more information at a news conference Sunday.

The Heenes spent much of the afternoon at the sheriff's office and were headed home where they were expected to speak to reporters.

Richard Heene has insisted that the drama that unfolded Thursday wasn't a publicity stunt. He and his wife reported that their son, Falcon, had been inside the flying-saucer shaped balloon when it launched from their backyard.

Six-year-old Falcon Heene sits in the box of his family's pickup truck outside their family's home in Fort Collins, Colo., after he was found hiding in the attic above the garage on Thursday. (David Zalubowski/Associated Press)About five hours later, Falcon was found safely at home, hiding in the rafters of his family's garage in Fort Collins, after the escaped balloon travelled more than 80 kilometres while being followed on live television.

Word of the impending charges was an about-face for Alderden, who previously said authorities had no proof the family was carrying out a hoax and that their reactions during the time the balloon was airborne appeared genuine to seasoned investigators.

He later said that he wanted to re-interview the family after Falcon said, "We did this for a show" in an interview with CNN on Thursday night. Falcon also got sick during two separate TV interviews when asked why he hid.

The Heenes are storm chasers who twice appeared in the ABC reality show Wife Swap. They said they were conducting an experiment with the craft that involved allowing it to rise about six metres off the ground in their backyard where it was tethered, but it came loose and floated away.

Military aircraft, including a Black Hawk helicopter that costs more than $4,600 US an hour to operate, participated in the rescue efforts for about three hours. Departures at Denver International Airport were briefly halted and air traffic controllers rerouted planes in the area.

With files from The Associated Press