Bangkok, Thailand | Tributes have poured in to the unstoppable Marc Marquez with the Spaniard hailed as "incredible" and "unbelievable" after he clinched his sixth MotoGP crown and eighth world title overall on Sunday.

MotoGP rivals, Marquez's own brother and Formula One greats joined a chorus of congratulations for the daring 26-year-old who dived under Fabio Quartararo on the final bend to win the Thailand MotoGP and seal the title in a pulsating last-lap duel.

The win gave him an insurmountable lead over closest rival Andrea Dovizioso, who was gracious despite another season in Marquez's shadow.

"We can speak and analyse all the things but at the end if you check his score it's something unbelievable," the Ducati rider told MotoGP.com.

Marquez has dominated the sport. Since 2013 he has only failed to win the world championship once -- in 2015. 

The 2019 title is his fourth straight and Marquez described this year as his "best" season ever. No one is disputing his assessment.

British rider Cal Crutchlow pointed out that Marquez has finished first or second in every race apart from one -- the Grand Prix of The Americas when a mechanical problem caused him to crash when leading on the ninth lap in Austin.

"He's an incredible talent," said Crutchlow, who is ninth in the standings. "I think he should just retire and give everyone else a chance," he joked.

Marquez is from a racing family and his younger brother Alex finished fifth in the Moto2 race in Buriram and is leading the class standings.

If there is a sibling rivalry it was hard to see in Alex's endearing tweet about his brother's achievement.

"Once again you leave us all speechless!" he said on his official account which showed a photo of the two brothers smiling after the win.

"In spite of your eight championships, you'll still be the 'little twerp' brother that you are."

With six premier-class titles, Marquez surpasses Australian legend Mick Doohan.

He trails only Italian great Valentino Rossi, who won the last of his seven championships in 2009, and Giacomo Agostini, whose record eighth came in 1975.

Rossi predicted he will break both.

"I don't think he'll struggle to reach nine," he told GPOne.com.

Spanish Formula One double world champion Fernando Alonso tweeted his congratulations, calling Marquez a "phenomenon."

Formula One driver Pierre Gasly, who attended the race before heading to Suzuka for next weekend's Japanese Grand Prix, tweeted: "What a race, what a battle in the last lap."

French rookie Quartararo, 20, led most of the way but was left in awe of Marquez.

"It's just incredible what he achieved, what he does with the bike," Quartararo told MotoGP.com. 

"He will be there for a long time."

joe/dh