(CNN) -- Davy Jones, whose charming grin and British accent won the hearts of millions of fans on the 1960s television series "The Monkees," died Wednesday, according to the Martin County, Florida, sheriff's office. He was 66.
A witness told authorities he was with Jones in Indiantown, Florida, when Jones "began to complain of not feeling well and having trouble breathing," the sheriff's office said in a statement.
Jones was transported to a hospital, where he was pronounced dead, authorities said.
A Martin County law enforcement source with knowledge of the case said Jones apparently suffered a heart attack.
Laurie Jacobson, whose company Living Legends LTD often booked Jones for Hollywood nostalgia shows, spoke with him two days ago about several new bookings.
"He was a vegetarian, and there was not an ounce of fat on the guy," Jacobson said. "He lived on the beach in Florida and ran miles every morning. This is the last person I expected this to happen to. He couldn't have been in better shape."
The diminutive vocalist and actor sang lead on the musical group's hits such as "Daydream Believer" and "A Little Bit Me, A Little Bit You."
Besides Jones, The Monkees included band members Micky Dolenz, Peter Tork and Michael Nesmith. The pop group was created to star in an NBC sitcom and capitalize on the Beatles' teenybopper popularity. "The Monkees" TV series premiered in the fall of 1966.
In terms of musical popularity, the project succeeded beyond anyone's expectations, with the group notching a handful of No. 1 songs (including "I'm a Believer," Billboard's top song of 1967) and four No. 1 albums.
The group, which was dubbed the "prefab four" by critics, rebelled against its management in an effort to take control of its musical career.
The move worked to an extent -- band members, who had generally been replaced by session men on Monkees recordings, were allowed to play their own instruments and contribute songs -- but coincided with a decline in the Monkees' popularity. NBC canceled the TV series "The Monkees" after just two seasons, and the band lasted for only one more year after that.
Though the TV show was never a huge ratings hit, its knockabout, Marx Brothers-style comedy -- inspired, to an extent, by the loopier sequences in the Beatles' "A Hard Day's Night" -- gained fans and followers, reigniting the band's popularity when MTV reran the show in the mid-'80s.
Demand for Jones at nostalgia shows was brisk, Jacobson said.
"He's been really busy," she said. "He's toured with his band, singing as well. He loved to pick up these little autograph shows. He loved the fans, he loved spending time with his fans. He often got on stage and performed at these shows. The lines for him were always out the door."
The Hollywood Chamber of Commerce said flowers in honor of Jones would be placed on The Monkees' star on the Hollywood Walk of Fame on Wednesday afternoon.
"That David has stepped beyond my view causes me the sadness that it does many of you," Nesmith posted on his Facebook page Wednesday. "I will miss him, but I won't abandon him to mortality ... David's spirit and soul live well in my heart, among all the lovely people, who remember with me the good times, and the healing times, that were created for so many, including us."
"His talent will be much missed; his gifts will be with us always," said fellow Monkee Peter Tork. "My deepest sympathy to Jessica and the rest of his family."
Beatle Ringo Starr issued a short statement: "God bless Davy. Peace & love to his family, Ringo."
David Thomas Jones was born December 30, 1945, in Manchester, England. He was already famous in his home country when he joined the Monkees. He had starred in the musical "Oliver!" on the London stage as the Artful Dodger and was nominated for a Tony for his performance on Broadway, according to a biography on a Monkees fan site. Indeed, he got a taste of the Beatles' popularity when the "Oliver!" cast appeared on "The Ed Sullivan Show" on February 9, 1964 -- the date of the Beatles' first appearance.
After the Monkees broke up, Jones enjoyed occasional acting roles, including a guest spot on an episode of "The Brady Bunch" and appearances in "SpongeBob SquarePants" and "The Brady Bunch Movie." When he wasn't singing -- he participated in several Monkees reunions over the years -- he was devoted to owning and racing horses.
Jones was married three times. He is survived by his third wife, Jessica Pacheco, and four daughters from his two previous marriages.
He told Britain's Daily Mail last year that he used to be 5 feet 4 inches tall, "but I've lost an inch."
He posted photographs of his horses, his grandchildren and himself on his blog, "Keep up with Jones," sometimes also posting messages to fans.
"I wrote some time ago that not everyone has dreams and hopes that come true," he wrote in a January 2011 message. "Mine have.
"Regrets, yes -- if you don't have them you're a fool. However, I thank all of you -- yeah, you -- for your support and love."
CNN's Alan Duke, Susan Candiotti and Louie Mejia contributed to this report.