Two Colorado parents jailed for falsely claiming their six-year-old son Falcon had floated away in a homemade balloon shaped like a flying saucer have been granted pardons by the western US state's governor.

Richard and Mayumi Heene pleaded guilty in 2009 to the "balloon boy" hoax, which became a worldwide media sensation with millions watching live as the silver helium balloon drifted through the skies for 70 miles (110 kilometers).

The October 2009 incident ended after five hours when the grounded balloon was found to be empty and Falcon emerged from a hiding place at the family home.

The husband and wife, accused by prosecutors of plotting to use the publicity to land a reality television series, were pardoned Wednesday by Governor Jared Polis. 

"It's time to no longer let a permanent criminal record from the balloon boy saga follow and drag down the parents for the rest of their lives," wrote Polis in a statement, saying the pair had "paid the price in the eyes of the public."

Law enforcement's suspicions were inflated when Falcon let slip in a CNN television interview that the entire episode had been done "for the show."

The hoax was seemingly confirmed within 48 hours of the interview, when Japanese-born Mayumi Heene reportedly broke down under police questioning.

But the couple's lawyer told AFP Thursday they only pleaded guilty to stop her from being deported, and had genuinely feared their son was aboard the balloon.

"They regret not checking this all out more thoroughly, but it was a coerced guilty plea," said David Lane. "And I think that also influenced the governor."

He added: "I can now finally say the balloon-acy has ended."

Richard Heene, handed a 90-day sentence for trying to influence a public servant, now owns a small business and has contributed to his community "by researching and educating about extreme weather events," wrote Polis.

Mayumi Heene, sentenced to 20 days in jail for false reporting to authorities, has become a naturalized American citizen. The couple now live in Florida.

Falcon, now a teenager, went on to form a heavy metal band with his brothers, Ryo and Bradford, releasing a song titled "Balloon Boy, No Hoax" and an accompanying low-budget video featuring a mocked-up flying saucer.